To me the NAD C275 sound great (maybe it’s just me)
but I like the sound. Great dynamics, details, excellent details (CD connected directly to the Amp., but I can’t control the volume).
Then get one of these for just $49 and you’ll keep that sound you like so much. Any active preamp will change that sound to maybe something you don’t like.
The Nad C275 has an input impedance of 100kohms so the Shitt Sys passive at worst 5kohms output impedance will NOT be compromised in any way, it will be the closest to what you heard direct, period.
The passive you used was most probably an impedance mismatch if you lost dynamics with it.
http://schiit.com/products/sys
Cheers George