Best upgrade option for this system?

I'm also looking into the Moon P-5. Any thought on how well this unit would marry with the Bryston?

Not that familiar with the equipment you've got, though I've owned Adcom in the past. With this said, I'd invest in a good integrated tube amp, Almarro or PrimaLuna. You'll be very much surprised and, quite likely, won't want to return to SS. I never believed this could be true, even for me, until I decided to jump into tubes.

I ran the comparrison test between my Adcom GTP-400, Bryston BP6 C and Conrad Johnson 14LS2. The difference between Adcom and Bryston was astonishing, made the highs much more inviting and brought out the midrange nicely.

The move from the BP6 C to the CJ 14LS2 was more subtle, but I did like the way it held the low frequencies lower and seemed to widen the soundstage.

I fell for the Conrad Johnson! But unfortunately it's a bit out of my $2000 enveloppe. This was my first audition, I plan to keep researching and continue testing until I'm ready to take the leap.

Audio Research seems to be coming up as another interesting tube preamp option for my Bryston 3B ST. I've seen references to the LS-3 on A-Gon, but when I look further, there are good reviews on the LS-15 and 16. I also saw references to SP series (not sure what the difference is). In my case, I would require a remote and I dont need phono.

Any thoughts / suggestions?