Suggestions for an affordable pre/pro

Also check out the Acurus Act 3 pre/pro, I've seen them for about $350-450 here at Agon.

First, your Adcom GFA-555 IS an audiophile component. I've had two for them for 20 years. You'll take them away from me when you pry them out of my cold dead hands.

All of your own ideas, and all of the suggestions offered above, sound reasonable. The question of whether to get a good used receiver (Denon 3805 comes to mind, if you can live with the weird remote) or go with a separate pre-pro is a tossup. The fact that you are on this website tells me that you will probably be happier in the long run with a separate pre-pro such as one of those mentioned above.

Yeah, from what you're saying, I'm gunna agree with the Acurus Act 3 choice. I've owned 4 of these over the years (don't ask why I sold em...it's complicated -lol). I've also had Macintosh pieces, Aragon Soundstage, "updraded" Act 3, Sony's 9ES pre, and the Krell 5.1 HTS. And, even though other more expensive pre's are "quieter" (you mentioned hiss - which the act 3 has a bit higher noise floor than others, but not manageable, IMO - and I've had 'em in small, quite rooms) for the money, the sound is powerful, clear, detailed, dynamic, and pretty musical! There's better, yes. But, for much more. And, for your needs, I think it might be a good fit.
But, you sound like you might be a bit more finnicky than some. In which case, your tastes/priorities will vary.
The Krell HTS, is as clean, detailed (for 20bit), and refined as ANY 5.1 pre'pro you'll ever find, period! Although there's NOTHING more dynamic than the Act 3!!!!
The modified version is a lot more (if you can find one, which I've owned) - which is richer sounding, more detailed, and just as dynamic! But, for like $300 range, you can get very acceptable (MUCH more dynamic, uncolored, nicely detailed digital 20bit sound).
System dependency always matters though. So tastes and systems might vary.
As for NAD, I'd check quality control, otherwise nice sounding, overall. The Rotel is dynamic, slightly recessed on top, a tad bland, but otherwise descent enough sounding.
The Anthem is descent, but I think it sounds a bit like the B&K, kinda warmish, not as dynamic, but fairly good balance, I think. The inteegra?..no experience.
The marantz AV9000, I've sold and installed before. It's, like the Rotel - descent.
What you won't get with these pre's are the new DSP room correction however. And, knowing nothing of your room, that could be very useful, so consider. In a perfect acoustical space, you wouldn't bother.

Hum. Don't know why the last post posted 2x's. Oh well.
Actually (and I've owned the Act 3,Upgraded Act 3, Aragon Soundstage, Krell HTS 5.1, Macintosh MX130 THX, Classe SSP25, and others), even though I've had and experienced "more refined" pre'pro's than the modest Acurus Act 3, I WOULDN'T HESITATE TO GET ANTHER ONE FOR A SYSTEM (OR FRIENDS) IN A HEART BEAT!!! It's just a darn good, amazing little 5.1 DD/DTS pre/pro! Clean, clear, uncolored, SUPER DYNAMIC, good soundstage, etc!!! (of course, digital connection is the only way to go on that unit, as it's all digital).
Hope that helps. Heck, I'm excited about that little unit right now, just thinking about it! (and that say's something).
(Also, why did I sell them before, if they were so darn good, you ask? Well because I got offered more for them than I paid! -money making comes first, ya know. Also, I had to try others to compare. So I traded)

Used to have an Outlaw Model 990 that I sold and replaced it with a Pioneer Elite VSX-74TXVi receiver that I use as a preamp/processor. Purchased mine a couple of months ago from Hi-Fi Heaven for $500 new. They had quite a few available in stock. You could use the built-in amps (140w/channel) that would have a better chance to keep up with your other components. Good luck with your search.