I’ve read somewhere that a significant part of it was that RCAs are easier to solder in an industrial setting.
Personally I figure in addition that although RCAs lead to more cables, at least you can easily see how they are connected. Two DINs may look the same but their connections may differ
RCA Phono sockets were cheaper and DIN wasn’t really much of a thing in the all-important US market, so when the Japanese came to dominate the audio landscape during the '70s they used RCA Phonos. It’s worth remembering that most UK manufacturers were still using DINs right into the '80s* until almost all succumbed to fitting RCA Phonos. A few, like Naim, DNM, Nytech and one or two others stuck with them due to their technical and performance superiority.
(*I recall the first version of the Audiolab 8000A used DINs, and of course, the A&R A60 used them throughout its life).
The term “DIN connector” alone does not unambiguously identify any particular type of connector unless the document number of the relevant DIN standard is added (e.g., “DIN 45322 connector”). Some DIN connector standards are:
A convenient multi connector to reduce the number of cables in a compromised installation.
Horses for courses use your ears. 
You are technically correct, but in the context we have here we are talking about a specific DIN plug and connector as used for sources by Naim… so yes we are using ‘DIN’ as a shorthand.
Yes, and worth remembering here that Naim only utilise DINs as connector, not as a connection standard. With Naim they are totally compatible with signals to and from RCA Phonos.
Again, here’s why DINs were chosen in preference to RCA Phonos by Naim;
From attached above FAQ.
The first difficulty with the RCA connector is that it has a high-frequency capacitive impedance of around 200 ohms;
This is not correct I’ve tested myself as well as cross referenced and I’ve found this impedance to be 25 ohms.
From Canare.
The usual RCA connectors are not made to have a specific characterstic impedance Canare says it’s about 25 ohms.
So does not have nearly ten times the impedance being claimed.
I used my ears too. 
I have always had to use a RCA > 5 pin Din 180 to connect my valve based DAC to my Naim preamp.
I completely subscribe to the Naim route of using Din as RCA connectors are sub optimal according to many reports I’ve read. Just take the example of a BNC cable at 75ohm. Experts say you cannot achieve this in RCA for the very reason that was suggested earlier.
What I would like to know is what Din socket is used on source devices like for example on the NDAC?
I was hoping to have this fitted on my source components so that I can begin using the hi-line cable instead of custom cables I’ve been using.
When I did my due dilligence before committing to Naim hi fi I heard that DIN is their preference because it is the electrical standard for signal and has better star grounding than rca
On YouTube look at the last five minutes of “how high end audio is made- factory visit naim audio” and u will hear Jason car explain why din is superior to rca for hifi
Indeed I remember it well, my first stereo amplifier used them as did our tape recorder and later cassette deck. As an impatient teenager, soldering leads on to the mono 3 pin variety of plug was ok, I was less keen on the fiddly 5 pin plugs required for stereo to and from tape machines.
And it’s untrue.
Sadly Julian is no longer around to argue with you on this.
No argument just facts.
Easy to test.
Too many excuses for cheap and compromised connectors.
I love my Supernait 3 but had I not had the choice of connection it would have been another brand.
By the way the guy in the video is called Jason.
To help us learn I think it would be better if you could describe what was better about your RCA interconnects than the Din alternatives?
Also how was the test carried out?
Read previous posts. 
As in was it an instant A/B comparison? How long spent with each interconnect before swapping.
Also ‘blew it out of the water’ isn’t a description of the sound. It’s your impression of the result.
Worked for me.
How long does it take.?
If you read all the posts you wouldn’t be asking these questions.
Nonsense argument.
I have and still my questions stand. You’re too quick to be rude and can’t address simple questions. Or perhaps it’s too difficult for you to type out an answer or more importantly you cannot articulate your findings
The comparison is described in great depth you’ll have to join some posts together.
Not trying to be rude but just deflecting your tone.
This link might help.