First off hello.
You are right in thinking the bartok and any dCS dac will be different to the naim dac’s you mentioned.
You will certainly get a much clearer and detailed sound. You will also get upsampling built in, DSD, many filters and different maps to choose from.
Plus very shortly new maps, and filters, plus 4 x upsampling. You also get to keep the old maps, filters, etc. They don’t disappear like how naim works.
But one of the biggest bonus is the built in volume control and different output voltages, this means you can run directly to Amp if you want. It works exceptionally well doing this as long as you match things to how you like it to sound.
I found that running directly into a 500dr from my vivaldi dac, sounded much better than with the naim 552dr pre amp. This brings me to something that might or might not bother you, if you run a naim pre amp it will hold the dCS back, lots on here have tried it and all found the same out vone to be true. The naim pre amps are very colourful you could say and its this that gives the naim sound, but it will certainly strangle the dCS dac and stop it showing what it can really do.
Getting back to the bartok, I know you will be buying into a fantastic British company like naim, but one that specialises in dac’s and this certainly shows. You also get great support going forward, and with the latest inpovements about to come out, you get free upgrades.
I haven’t looked back for a second since I first heard a dCS dac, I went to upgrade from my NDS with 2 x power supplies to the ND555, and luckily I got to experience the dCS range, I soon forgot all about the ND555.
But only you can decide, plus if you have a complete naim system at the moment? I would be prepared to say that it won’t last long once the bartok joins it, as you will start to see what you have been missing for years and in turn that will bring changes to full enjoy what the bartok can do. This is the biggest mistake other naim owners do, they use it in a naim system and that doesn’t really work.
Enjoy the ride what ever you decide.
Cheers dunc