So I tried NAD as PreAmp. The chain was BubbleUPnP/HiFiCast on Android device as Source-> RPi Zero running Volumio as Renderer->Toslink input to CA DAC Magic Plus(switched to pure DAC mode, no more digital PreAmp)-> NAD C320 (as PreAmp)-> Crown XLS1502 running L and R channel, High passed to 100Hz, Crown XLS2502 running 2 8inch Polk Audio Subs, band passed to 60Hz to 150Hz, 2 12inch Subs, Sony and JBL, low passed to 60Hz and below.
Now RCA out from DAC went into Aux In of the NAD and Pre Out of NAD went into Crown XLS1502, which fed 2502 too through Link out.
Initially, there was a lot of "chattar pattar" and hiss. Thought cables to be the issue so tried different pairs of RCA. Same thing. Then I reinserted the coupler that I was using to feed PreOuts to Power IN. As it has a female RCA out on it, I attached the RCA for Crown AMP to it. This time, the noise died down significantly. I say significantly because the "Crown hiss" was audible as I had them cranked up to 9 out of 10. Turned them down to 75%, and it was a quieter room.
Started playing tracks, knew it would sound good as I had a similar setup when I was using just 1 Crown amp for Sub duty and the NAD Integrated for full range L-R work. But this time there was something different. 2 things became immediately evident. The NAD effect of warm sound was perceptible even through Class D Crowns, and the transparency of Crowns themselves was obvious. My bright and sparkly JBL coaxial were starting to sound like a pair of Wharfedales. The soundstage got a fresh breath of life, with each part, each component being played in full. The drums, the cymbals, all were there. And with that, the shortcomings of CA DAC became evident. While my earlier Topping E30 almost brought Shreya Ghoshal to my room, with no ulterior motives, the CA DAC was not doing justice to mids. The Highs and Lows were good, tight, but the mids, that electronic guitar, it was down right muddy in some songs, songs which I have heard earlier too and knew sound good and were in lossless format so file and recording quality weren't an issue either.
This little experiment made me realize 2 things; how much a good active PreAmp can help to liven up the sound, and the other being that I need to get a better DAC.
Want to share a couple of short clips that I made of it, but don't know how to do so. If anyone can point me in the right direction, will post them next here.