If you are using a DAC now you may be able to get more for your money by just getting a DAC upgrade.

When I first set up my Adcom system, gtp-450/gfa-5400, I bought a used Denon CD player, it was an upper end unit but a couple years old. The system could get a bit bright especially at high volumes and in a live room. I eventually put a solid state Conrad-Johnson DAC in the loop and it made a tremendous difference in sound quality. So I do think your system is good enough that you will appreciate an upgrade in digital playback whether DAC or single box. That ole Denon is still chugging along and made a great transport. The system really came into it's own when I recently put the 5500 in. I too really find myself liking those old Adcom amps. The 5400 is alright for the money but I can take it, or leave it, but I don't plan on parting with this 5500.