What type of preamp

I would suggest some with tubes.

You are where I was a while ago it looks like your system is pretty well matched now. Yes buying a pre would help but the pre has to be better than the NAD. I had a Audio Reasearch SP16 tube pre with a HT bypass I used that instead of my denon for 2 channel and put it on bypass for HT and suddenly it gave my system a warm smooth tube sound with more sound, I didn't realise how much the solid state receiver was cutting out. Will it make a difference you will just have to try.

I keep on looking at your system to see where $$$ could help and you are definally at a point where you need to break out of the solid state best buy componment. But there are several areas you can start the pre is not a bad start. I don't think byamping out of a receiver or 2 different amps is a grate idear. You are better off with one good amp. May also want to play with cables/wires a bit I didn't see what you were using.

A better CD player is a more worthy upgrade than getting a new preamp. Consider a used Rega Planet 2000 for about $500 or a used Jolida 100 for about $650. The Jolida is a real good CD player and will hold its own even if you upgrade the amp and preamp later.

The CD player is the weakest link in your system. I owned both the C521BEE and the C320BEE before.

You might try to find an Audio Electric Supply AES 3 tubbed pre made by Cary. Find one used and be sure not to use the original Chinese tubes (I like my Sylvanias) and if you don't like it resell it and you shouldn't be out much if any.

Check out the Audio Experience Symphonies Plus Line Stage from Ys Audio. High quality parts and a nice sounding unit to boot. I've been very happy with mine.

I believe source first for your system.

I own a Pioneer DV-565A universal player with Trichord Clock 4 and "Never-Connected" digital power supply mods. I wanted to install an LC Audio ZapFilter 2 (a complete and very high quality analog stage) but the 565A chassis was too small, so I went with cap/diode analog stage upgrades. For about $1000 such a player is phenomenal. Mine is dead quiet with impeccable detail retrieval/soundstaging and very non-fatiguing.

Sound Odyssey on 'Gon offers a very similar mod package to the Music Hall CD25 and, I believe, Brice can install the LC audio ZapFilter 2 (he said so by email to me a while back). The Music Hall CD25 has a better transport mechanism than my Pioneer (though its CD only). A Music Hall CD25 with Trichord Clock 4 and 'Never-Connected digital PSU along with an LC Audio ZapFilter 2 would be a fabulous CD player. I have no affiliation with Sound Odyssey, just a great admiration for what these particular parts upgrades will do in an affordable stock CDP to raise it to a very high level. Not all mod packages are the same.

I've owned both tube and ss active preamps from $400 to several thousands and feel that lesser active preamps have too much veiling of detail. If you want to keep your CD player and it has high enough output with short IC run to your preamp, I'd suggest the DIY HiFi Supply Django passive transformer-based linestage with S&B transformer (about $1200 already assembled). I own one and it is absolutely transparent. It will also tell you more about the quality of the other components in your system, which may be good or bad for now but ultimately a very good thing.

Best wishes whatever you choose.

jb

i would keep any upgrades in the nad family. you're doin' fine.

source first then dedicated preamp.