These things can only be either because something regarding the DAC has changed (e.g. changes in the noise affecting the DAC) or because you expect something to change and so hear it. The latter is not a criticism of you or your hearing. We are very susceptible to such things - as has been shown many times in many situations. It cannot be changes to the actual digital data going into the DAC - any changes there (if changes were possible) to the data stream would result in random and very unpleasant changes to the sound - not in terms of changes to the stereo image, or bass texture etc. That would imply a more structured change to the data than RF noise would make.
Do you sometimes get drop-outs in Digital Audio Radio (if you have it) or in Freeview (if you use it)? We certainly do, particularly with Freeview. It results in fairly large pretty random blocks of random colours on the screen, and very unpleasant screeching sounds from the audio. That comes from the data stream being interrupted or corrupted. You would expect similar sorts of effects if ever the audio digital stream were seriously affected by something.
Have you seen any of the lectures by Floyd of Harmon Kardon on auditioning loudspeakers? It makes very interesting viewing.
Similarly have you listened to the many audio illusions available on the web? For instance, two notes of differing pitch, one following the other, can be interpreted either as rising or as falling pitch by different people. The wetware we operate with is very easily fooled.
Ok ā¦ we will agree to positively disagree ā¦ there is not point me saying any more. 
I guess masked by whatever is going on in the DAC (possibly modulation of a sort) when RF noise is present while the digital audio stream is being converted to analog.
By way of comparison with a different source but I think similar effect: when I first fed the USB output from a computer renderer into a Hugo DAC, the music sounded good, though not outstanding. When I routed the signal through a very good RF isolator before Hugo it was as if a veil had been lifted, with greater clarity revealing more. The computer USB output undoubtedly would contain significant RF noise superimposed on the digital music stream, while Hugo does not incorporate effective RF blocking. That same USB output into Dave DAC is crystal clear - but then I understand that one of the key optimisations in the design of Dave was RF rejection.
Thanks IB I am clearly not going madā¦ 
No you arenāt 
Iāve found the same thing as have others listening to the system. There are various theories why, some more plausible than others and none of any interest to me: I just listen to the stuff, not make it!
My seat of the pants ā¦ theory (which may be wrong!) is the rfi and electrical hash ā¦ is so loud that it drowns out low level detailā¦you donāt hear it as it is outside the human audible range + the electrical circuits themselves roll off at ultra high frequenciesā¦but the dac is exposed to the lot ā¦ its almost as if the uncorrupted bits are being broadcast in a fog horn of noiseā¦and anything you can do to reduce that allows the dac to resolve moreā¦ (I am now ready to be shot to pieces! 
)
Apart from the hyperbole, you may be right to a greater or lesser extent depending on the equipment.
I wanted to say that the transport was being considered as less important as today, because at that time the Dac were connected to simple mini cheap laptops, in high end systems.
Melco, Innuos, Antipodes, transports / servers ā¦appeared much later.
I personally donāt think that the Dac is the most important, a bit more important in the digital source, but you have to consider the quality of the entire chain: transport / server, quality of the cable, network isolation.
I mostly agree - DACs were consumer items for a while, shoved into PCs and personal digital players without too much worry about how good they are. But I would say that they are more important than the source - so long as the bit stream and timing are correct then Iām not sure what the source can add in terms of sound quality.
I found that source can add a lot. From files on a noisy pc to unitserve to unitserve with linear ps to Melco n1/2 , I found at each step an upgrade in the quality of the sound. The same as going from cd5i to cd5x to cdx2.
Itās not illusion or brain fooled. The improvements are clear and real.
So e of us like to know why, not just know (and this is nothing specific to this hobby), but indeed we are all different and not everybody is interested. However, understanding cause can help find cures or prevention, or help focus attention where it may be most effective.
Meanwhile blind testing of things being compared can eliminate the psychological influences that inevitably sometimes come into play and help reassure that we are not being misled or unintentionally misleading ourselves, so I commend it - most especially when trying something new with an expectation that it will be better or worse.
I have experienced the difference myself. I donāt know why, but its thereāpositively.
My work is in Astronomy, and like most fields, it starts with an observation that is odd or puzzling. Its followed by thinking and postulating and research, and then someone publishes a theory on why. It gets reviewed and duplicated and shot down sometimes, and corroborated other times, and it serves as the basis for some additional theory. Same thing hapnens in all science. We start with nothing but observations. Theory predicting things is a small part of the landscape. Explaining what we observe is a major part. Audio is no different. Thanks for posting your observations.
I am with you apart from this bit - depending upon what you mean. Prediction is a really important part of science. Theories that donāt have testable predictions are, possibly, interesting but are only theories in the common or garden sense of the word, rather than the scientific sense. Of course, in many areas of science it can be difficult to predict something from a theory - for instance, in archaeology which is almost entirely observation and theorising, though sometimes prediction is possible and valuable.
I can hear differences too even with a modest Muso-2. Iāve done a straight run from my switch (cheap TP Link), WiFi and today Iāve isolated the Muso-2 by putting a pair of Fiber Media Converters between the switch and the Muso. There are differences I can hear. Fascinating stuff.
Re: the optical fiber attenuators Iāve added to the cable before the receiving opticalModule - I finally figured out the sound Iām now hearing and where Iāve heard it before. It sounds as if itās being played directly off the mixing board after being recorded. The detail and clarity is that crisp, as if itās only one generation removed from the actual process of recording.
That said, it sounds a little lean and bright in my system (though I think the culprit may be my little beloved 110 as itās now being āout-sourcedā so to speak) but all of the instruments come through so much more distinctly. And, despite it being leaner and brighter, itās also less fatiguing at the same time (as long as I donāt play too loud) which was a surprise to this tinnitus suffer who likes nothing bright. Early days yet, and I have another pair on order to try at the other end to see if that makes any difference. Iām hearing reports that the fiber cable quality can make a difference as well - ugh.
Thats a very good description regarding clarity of sound ā¦
This subject has been discussed so many times beforeā¦ i donāt know what all this talk of ātheoriesā is aboutā¦ what i do know this is about standard engineering design considerations around EM disturbances from ethernetā¦ and here, as I started posting several years ago, is a Texas Instruments engineering design paper on handling and mitigating fast ethernet induced noise from cables and other effects into hosts. This stuff really isnāt rocket scienceā¦ 
Its kind of like saying there are theories on how internal combustion engines workā¦
http://www.ti.com/lit/an/snla107a/snla107a.pdf
Of course many electronics manufacturers have similar approaches - I only refer to TI, as Naim use TI DACs in their streamers. Oh yes you can see this is nothing to do with ābitsā or ā1s or 0sā or other such abstractionsā¦ which donāt directly correspond to Fast Ethernet in terms of physical symbol encoding .
Excellent very goodā¦ a bit technical for me but point taken. I think we are all agreed reducing noise (possible jitter?) is a good thingā¦
I agree that prediction from theory or models is most important. What I meant to say is that its been my observation that pure theory generated without observation is a small part of what happens. Sometimes that happens first, then observations that do not match, and then a revised theory/model is developed. My experience is that observation that is not in accordance with exisiting theory drives a majority of the discoveries of new models and theory and understanding.
Bailyhill
Hi ethernet clock jitter possibly - but this shouldnāt be confused with sample rate jitterā¦ totally different and unrelated