I did a demo A-B comparison of the Marantz 9500 ($2000) vs the 2-channel Marantz SA-11 ($3500) with Redbook and SACD's and the differences were very very minute. This was on an ultra revealing high end system made up of Burmeister amplification and B&W Nautilus 802D's with top of the line Tara Labs cables. The SA-11 bested the 9500 in both Redbook and SACD, but it was only while really critically listening to higher frequency stuff (tamborines and the like) that you could overtly tell the difference. The bass was a bit more defined on the SA-11 also. These slight differences were not worth a $1500 margin in my opinion.
In the end you'll have to specify whether you want the video capacity or not on a player like the 9500, whether you want multi-channel capacity or not, and also what your exact budget is going to be. The Denon, as Gunbei mentioned, is a favorite with modders, but you'll also have to pay extra for that stuff, and some of the modders take a while to get your unit finished. As far as I know, none of the modders are tinkering with the 9500, but put a few bucks in their pocket and at the very least they'll swap a few things out for better quality parts.
In the end I opted for the lower priced Marantz 7600 ($1000) for my HT setup. It plays all the formats and even has HDMI out for DVD watching into my plasma. As for a reference digital front end, I too want a 2-channel universal player, with the video circuitry disabled...or non-existant. The modders have that market all set up for you if you want that kind of player (meaning NO video and NO multi-channel).
Last but not least, there are also a few stock 2-channel universal players trickling out that were designed to be video-less right from the get-go. Ayre has a $6000 box (outside of my price range), and then there are others....
Good luck. Sorry I cant speak more on the Denon, other than it being great fodder for the aftermarket modder community.