John,
I don't think you'll be seeing decoding of next gen audio codecs like DD+, DTS-HD and Dolby TrueHD in receivers and pre-pros any time soon; i.e., at least for a couple of years. For the moment, the industry prefers that those codecs be decoded in the hi-def players and set-top boxes. The decoder chips will (hopefully) have more extensive bass management and time alignment features than current SACD/DVD-A players do.
The multi-channel signal can be transmitted three ways to receivers and pre-pros: 8 channels of 96/24 PCM (via current HDMI 1.1) or 5.1 channels of 640kb DD (via SPDIF coax or optical) or as 8 analogue channels (via...well, 8 interconnects). Your 990 is already capable of doing the last two, so you're set.
TrueHD (dumb name - people are going to abbreviate it to THD and then make fun of it) uses Meridian Lossless Packing as its core. Imagine MLP with its DVD-Audio restrictions removed: e.g., no longer limited to 6 channels.
Dolby has also included DD features like DialNorm and DRC (dynamic range compression) as well as extensive metadata for things like good sounding downmixes from 7.1 to 5.1 or 2-channels (assuming the recording engineer knows how to set the downmix coefficients properly). TrueHD even has the ability to piggy-back a DD stream, since there is plenty of room in its 18Mbps data rate.
I wish they had stuck to the codec's interim name: Dolby Lossless. Two words that describe who makes it and what it is. I guess it made too much sense to keep that name.
Anyway, a list of TrueHD's features can be found
here .