Yes the Ortofon 2m red mm cart is not the best mm cart around and some find it bright and sibilant. And yes it sound sibilant with my former Rega fono mm preamp. But i heard it’s punch, openess and lively character i like. But the sibilance (some records more than others) made me bonkers.
Than i thought hmm a preamp with high input capacity can dampen that nasty brightness. And a mint 2e hand 2019 Stageline N does the trick (470 pF input capacity). The SL N is connected to my Supernait 1 aux2 connection. The 2m red has become very listenable and vinyl now has the grunt and attack i liked from the ND5xs or CD5si. With a AT VM95c the sound was good with Rega fono mm but always missed dynamics, attack and grunt compared to my digital gear. With 2m red there it is for me. Furthermore the SL N is dead silence with no hiss or humm, that will make it sound dynamic i think. The AT VM95c also sounds good with SL N but has less punch and sounds a bit too safe.
So vinyl now is a joy to listen again. And the refurbished Denon DP60l is a joy to operate.
One that is designed to be used with a high input capacitance (arm leads, arm cable, phono stage).
The Red is designed to be used with a somewhat lower input capacitance than the Stageline so the Stageline will roll off the high frequencies which is probably what the OP likes about the combo.
I agree but we all hear slightly differently and have what our ears pick up interpreted differently by our brains. What is good for me may not be good for you etc.
Often the trouble with variable loading and capacitance phono stages people think that if it does not serve exactly what their cartridge specifies it will not sound good. I have demo’d such stages to people not telling them what has been set and often they prefer a different combination to the obvious. I tell people to try them all and listen for what they prefer.
The 2m red was a big surprise for me when I fitted one to my Project turntable. I wanted a really cheap MM cartridge just to get me up and running temporarily while I decided which MC to buy. It’s taken me 2 years so far and the 2m red is still there and will remain so until I wear it out. Of course it will be replaced by the 2m blue but for now it’s one of the best bargains out there imo. It’s not perfect by any means but it does the job very well in my modest living room system coupled with a Project phono box s2 into 5si and Emit M10s.
But with Stageline connected to aux2 there is a slight deterioration in soundquality with the CD5si and ND5XS sources. Most noticable with CD5si. Why is that?
Using powered output from Aux? Siphoning off the preamp power rails is one concern. But might also be worth checking that either your Naim CD player or streamer (and only one) is set to chassis earth. If they ate both set to floating, the phonostage might introduce ground noise with nowhere to go.
Are theories. I’ve not noticed any deteriorating of quality since connecting the StageLine.
I don’t think you mentioned if you’re using the powered aux2 socket?
Have you tried powering the Stageline with an external power supply, such as iSupply/Flatcap/Hicap, instead of using the powered aux2 socket?
If so, while using the unpowered aux2 socket, the problem remains, then perhaps a grounding issue?
If it becomes solved, then perhaps it was a power draining issue (from using the powered aux2 socket) as mentioned earlier?