I wanted to share my experiences with this user community about the wonderful NAD amps that we have or used to have. We all know that NAD amps are great value for money. They have a very good sound too. We chose them because of their neutral character (maybe a tad warm). I found NADs to be a bit laid back, which is a very positive thing for me. Eventually there comes a point in our hobby where we feel that we need to upgrade. We start looking at other high end brands and eventually make a shift. I went through this cycle. But fortunately for me, I did not have enough resources to go to a megabuck amp. So I decided to go the separates route with a step-by-step option. I don't know how many NAD owners notice this, but the NAD power-am section in an integrated amp has great sensitivity (< 800mV). I was not aware of this. I found this info, and the importance of it, while researching for preamps and power amps. My research led me to Promitheus TVC. This is like a passive preamp that does not have a power supply of it's own. Instead it attenuates the incoming signal from source (CD player/DAC/etc). It's output is fed to a power amp. TVCs do not have impedance matching issue. But gain is important for them. So your source should deliver atleast 2V for the TVC to work fine, while the input sensitivity of the power amp should be < 1V.
Long story short - I have been using the TVC with my NAD for a few months now and can confidently say that this combination is nothing short of stunning. The sound stage, depth, seperation and naturalness to instruments and voices are affected in a highly positive way. The TVC burn-in also critical. It should burn in atleast 200+ hours. This is when the magic starts. It is unbelievable that the NAD's power amp section can handle this much "more" info that never showed up when used with the built-in preamp. A thought comes to my mind that besides raising the power ratings as we go from NAD 315 to NAD 372, it is the passive preamp that NAD upgrades bit by bit as we climb the ladder. But the in-built preamp (passive I guess) is no competition to the TVC.
I have no affiliation to Promitheus. But as a satisfied and happy owner of this combo, I wanted to share my thoughts with this community. YMMV. I will upgrade my amp as and when I have some funds - after all this is a hobby!! But in the meanwhile I am glad that I picked up the NAD over other integrated amps.
I have use a Nad amp (first c272 now c275) with a a passive pre (ft audio little wonder) for a few years now. I like the set up and it sounds very good. I just wonder how much range you have on the volume knob with 24 steps? I don't have much range and I don't have a stepped attenuator. But I do think that if you can swing it a passive pre does have much to offer.
The power amp in NAD C352 integrated is pretty sensitive at 770mV. Out of the available 24 steps I get very comfortable by 10-11 position depending. I rarely have to go beyond 12-13. One thing I noticed that during the initial periods I had to go between 11-12. But now that the TVC has gone through the break-in, it is a altogether different animal. "SPACE" "NATURALNESS" is what comes to my mind as I sit here listening to Diana Krall's Live In Paris and trying to respond to your question. BTW my TVC is the Reference C-Core.