Upgrade from Adcom GFP-750?

Having recently added a Bryston 9BSST, I'm thinking about upgrading from my Stan Warren modified Adcom GFP-750. I've been pleased with my Adcom's sound, flexibility and reliability, and I think I'll be even more pleased when the modified unit arrives. But I'm wondering if and how much better I could do within my budget (~$1500, used). I'd prefer to stay with SS. The main contenders are the BAT VK-20, Bryston BP25, and Conrad-Johnson PFR. Would any of these, or others not on my short list, represent a significant upgrade in sound quality? I appreciate your comments and suggestions.

Adcom GFP-750
Bryston 9BSST
Linn Ikemi
Thiel CS2.3
Kimber KCAG ics
Acoustic Zen Satori cables
Did you use it on passive or active mode?
Are you willing to get better preamp that still has both?

For active preamp Plinius M14 or Pass P can be your choices.
I moved from the Adcom GFP-750 to the Sim Audio Moon P-5. I've been delighted with the build quality and the sound. It offers all the transparency (and then some) of the Adcom in passive mode, yet has wonderful dynamics as well. It certainly is a remarkable unit.

Good Luck!
I agree with Marakanetz on the Pass Aleph P. Very nice pre with the same low gain as the gfp, but much nicer sounding.
yet you should stay away from bryston bp25. to my ears that's probably the worst gear they ever produced so far. it will certainly be a downgrade from adcom.
Well, you are already using a Pass design, so perhaps Pass for the upgrade. Price point is a little off--about $2200 on the used market for an X2.5 or X1 hybrid. I upgraded from the GFP-750 to an X1 and I am very happy.
I used the Adcom both active and passive: active for rock, electronic, ambient; passive for jazz, classical, acoustic. I might be willing to increase my budget to retain the flexibility of both options.
You definitely like your Adcom. I think you'll like an Aleph P even more-the Adcom has a circuit design by Nelson Pass, the Aleph P is an all Pass Labs design.
I'm selling my GFP-750 & tomorrow I'll install my Pass Aleph P. It will stay in my system until I try a Pass X1 & come up with the money for one.....
Lmack,why not try tubes? I recently tried a tube preamp to mate with the 4Bst and found the sound quality amazing. Tube preamps let you fine tune or critque the sound that you are looking for by interchanging tubes or tube rolling as some might say. Dont discount tubes to give your amp exceptional upstream data.
I'd hold off until I let the Stan Warren mod burn in for a few weeks. The Black Gates he uses have a long "gestation period." Other writers have suggested good options that will always be there.
You're right, Ivanj, and that's what I'll be doing. But I still like to explore the possibilities, in case something very attractive comes up used. So far, I like the Pass and Sim possibilities, even if they would mean stretching my budget a bit. Any more suggestions would be most welcome, and thanks all for the suggestions so far.
Honestly Lemack, For the price you mention,I cant think
of any preamp that can beat this.When I replace my silver
cable to cardas golden cross balance, every breath of this
unit came out, no wander this unit is a Stereophile Class
A unit.Bryston wont go near this adcom. Try to use the
balance and try it will full sounding cable like cardas,
audioquest, because this preamp if you put silver it will
give you leaner and slight brightness.You dont even need
to spend $1500 if you hit jackpot on the right ic,just
be patient.