Looking to Upgrade Amp & Preamp

I'm looking to upgrade my amp and preamp.

Amp: Adcom GFA-555
Preamp: Adcom GTP-400
Speakers: NHT 3.3
CD: Rotel RCD965BX

I listen primarily to rock, jazz, and electronica. The Adcom amp and preamp have been solid workhorses for me since 1990, but if they can be improved upon significantly within my budget, then I'm interested in upgrading.

Preamp requirements: (1) phono section unnecessary but if it's there, it's a bonus; (2) integrated tuner would be a plus, but not necessary; (3) five or more line-level inputs; balanced input/output a plus for future flexibility; (4) this being 2004, a remote would be nice; (5) solid construction; something that will last for decades, ideally; (6) good ergonomics and stylish appearance a plus (prefer black to silver); (7) surround sound is completely unnecessary and undesired. And, it need hardly be said, I want the best sound I can buy within my budget, given the above constraints. I'll spend up to $1500 for the preamp.

Amp requirements: enough muscle to drive the NHT 3.3's at least as capably as the Adcom GFA-555. Substantially better sound than the Adcom (otherwise there's no point to upgrading). [Inasmuch as the Adcom does not have any glaring deficiencies that I can hear, I cannot specify what 'better sound than the Adcom' means, but surely some of you have opinions regarding what specific improvements are achievable at my price level.] Ideally, it should be built like a tank, just as the Adcom is, and should be something that will easily last for decades. I'm willing to go as high as $2000 for the amp, *if* I am convinced that the sound improvement is substantial relative to cheaper equipment.

So, any and all recommendations are welcome. I'm perfectly happy to buy used equipment in order to get more bang for the buck. So far I have been looking into various models by Rotel, Adcom, Classe, Krell, and others, but there must be hundreds of manufacturers out there, and I need to narrow the scope to a handful of choices that are likely to be among the best bets given my requirements.

Thanks in advance for all suggestions.

-jbiii