Upgade... Amp choices???

After auditioning the B&W naut 805's with my system and hearing very little difference a discussion with my local dealer indicated that I need an external amp for my mains. Present system consist of Denon avr2800, Onkyo Integra dvd, and Polk bookshelf (can't remember no. but tweeter and 2 5.5inch mids) that sound very good for their age, Velodyne 10 inch sub. The biggest disappointment with the system is having to play at high spl in order to obtain feel for the music. Low levels everything looses focus and seems to blur. No soundstage and very flat. The search is on and I have found these amps that interest me but there is no dealer local for me to demo any of them.

ATI 1502 150wx2, Belles 150A 2x100 (?),McCormack DNA 0.5 100x2, Rotel RB 1080-2x200.

For the immediate time will be using the Denon pre outs to the amp but I will, in near future, be adding a pre amp and am leaning to Magnepan mmg's or aci saphire III le for speakers. Want to get an amp that will provide speaker flexibility and have the ability to maintain dynamics at lower volume. Price wise will be buying used and all of these fit within the budget(around $600-800). All suggestions appreciated.
Hi Scoly; I can highly recomment the McCormack DNA-0.5. It has great bass and is definitely stable into 4 Ohm loads. It was Stereophile Class B for years. I saw one here on Agon for (I think) $750. yesterday. It's definitely worth tracking one down, and it's an excellent sounding amp. Cheers. Craig
Check out the Stratos from Odyssey. This is one killer amp for a very reasonable price. This amp received great reviews from all of the Stereo Mags. I noticed a huge improvement over my Carver amp.
While Belles has a good reputation, I, too, cast a vote for the McCormack amp. Admittedly that's coming from a big fan of their products. In any case, the 0.5 is a tough act to beat for the money and an upgrade path is avalable via SMcAudio (www.smcaudio.com), a company started by Steve McCormack. See the Web site for more info.
I also think you'll be happy with the McCormack. I had a DNA1 Deluxe and was very happy with it (driving difficult loads... Apogees and ML CLS's. The .5 has a similar sound and almost as much real world juice. I have heard the upgrades that Steve does and they are fantastic. You won't go wrong.
I'm surprised you heard NO difference between a B&W N805 and Polks. Even with a receiver I would think the B&W would sound different. Perhaps you meant the B&W did not sound better. I own the N805's which I'm selling on ebay (shameless plug) and I think they would sound better than Polks even with a Receiver. However, we all have different ears and perhaps the B&W are not for you. Try another high end set like the Dynaudio 1.3SE', ProAC 1SC, or even Soliloquy 5.0's.
Sorry didn't finish. If you find these speakers better buy them or the others you mentioned and then perhaps invest in an amp. While others may disagree, I find the difference between speakers the most obvious. The differences between amps while definitely there are a little more subtle. By the way, I do agree with the others in the list you gave, I would go with the McCormack. However Maggies do like power and I don't know enough but will ask others if the DNA 0.5's will drive them the way you want.
Thanks to everyone. Looks like the McCormack .5 has a consensus. Must be everything the reviews say it is. P_mmk I agree it is strange not to have heard a difference and I should have been more specific. We were running both sets of the receiver and a/bing. Almost every time we heard a significant difference it was the Polk's that we thought sounded best. Seemed almost impossible to me because I love the look of the 805's and thought they sounded great in the store. I wanted the 805's to be the choice. Needless to say the employees and owner of the store were floored when I walked back in with them. They had told me that if I took them home they would never be back. Really wanted to ask them to come over and hear for themselves but already know what they would have said. As for the speakers yoou mention they are not available here. Small town with only two higher end stores. Paradigm, b&w, theil, phase technology is about the only choices locally. Will have to rely on reviews and kind responses from folks on the boards for speakers. Definitely want to take the next step but its one at a time for me.
Thanks again for the help and suggestions. If there are other amps I should consider feel free to mention.
FYI I have seen a bunch of DNA-1 (non-deluxes) lately going for as low as $800 over at audioreview marketplace. Had one for a long time and loved it. A/B'd against that rotel and never looked back.