Diagnose the weak link.

I have a very similar set up: Sony 5400, Thiel 3.6s, Parasound Halo A-21. I recently borrowed a used Audio Research SP-17 line stage from a dealer and was very happy with the improved dynamics and cleaner bottom end (nice phono stage, too). Unfortunately, I couldn't work out a good price on the preamp, but I did find a nice deal on an SP-16, which will be here next week. Like others have suggested, I believe that adding a high quality tubed preamp is going to help a lot with your Thiel/Bryston combo.

A couple of additional thoughts from my own experience. The Thiels have a very strong mid-bass that can easily get out of control if your room isn't ideal. Placing the speakers along the long wall of my room really helped clean up the bottom end.

Also, don't expect much forgiveness from your current set up on badly recorded, over-compressed rock albums...even with a better preamp. Good luck.

"although I wish I could find a CJ in black that would match the look of the Bryston 4B"

Black and gold is a nice color combination, IMO.
Glad you’re losing the NAD.

If your system only consist of the CD player, speakers, amp and pre-amp and if your CD player has an internal volume control, then take the pre-amp out of the circuit altogether and run the CD player analog output directly to the amp. If you want a pre-amp because you have other sources, then a different pre-amp may be the way to go. Also, I can guarantee that your analog output from the CD player is not up to snuff and a DAC will dramatically improve your CD player/transports sound.

For most CD players, the internal DAC is a weak link 1) because they are not typically as good as the digital circuitry in a stand alone DAC and 2) the power supplies are inadequate for the analog output stage.

I'm not sure if your Sony ES unit has a volume control, but if it does, nix the pre-amp if that is your only source.

enjoy

I would consider a Modwright 9.0 pre. My 4bst works nice with mine.