The Sony 550 might be the way to go, if it has 7.1 analog output. Having said that, I have a few more thoughts about the Panasonic vs. Denon question.
Is the Pro Logic IIx format significant for use with the 990? I don't see any support for this format in the Denon either. If the Panasonic will end up being as useful as the Denon I'd rather use the jumpers (y-connectors?) with the Panasonic.
The 990's 7.1 Direct input (as with just about every other receiver or processor's multichannel analog input) bypasses the processor's DSP section - the 990
does offer bass management, which is rare, but it doesn't offer surround processing. That means that if you want to expand a 5.1 source to 7.1, you need to do it at the player - which is where Pro Logic IIx or something similar comes in.
I would rather have profile 2.0 but I'm not sure I'd use it for anything other than updates. I'm really not a gamer.
I don't know that profile 2.0 will have a lot to do with games. It will have more to do with things like downloadable content (extra commentary tracks, bonus features, and the like). The only HD-DVD that I've seen use this (in my meager connection of HD-DVD's) is Transformers. It's not necessarily going to be a terribly big deal.
I don't have the technical expertise to know if the Denon is a waste of money or not. I prefer Denon to Panasonic but I don't want to waste my money either. If the Panasonic is more compatible with the 990 then I will go that way.
I see the initial Denon Blu-ray player offerings as a way for Denon to finance some R&D. The feature set for their top-of-the-line player (the one that you need if you want multichannel analog output) is really not substantial enough to justify the $2000 price tag. By comparison, I think that Panasonic is going back to their early DVD player days - from 1998 (when I got into DVD) until around 2002 or maybe even 2003, I recommended Panasonic players to anyone who asked me for help in shopping. They were competitively priced, had good feature sets, and performed very well (no chroma bug, which was a big deal at the time). Starting around 2003, their DVD player offerings took a real hit as players became commodities ($50 players at the grocery stores...). With the BD10A and BD30, they are looking more like the Panasonic of six or eight years ago.