Hopefully Gonk or someone who's good at explaination can take the time to answer this question, which I'm sure most of you will find basic, but I'm new to DVD-A....

My Oppo DVD player (I think you have this deck too, Gonk?) has 5.1 analog audio RCA out jacks (6 total...well, actually 8, but two are labeled "mixed"). Of course, it also has digital out jacks, both optical and coax. My question is, if I want to listen to DVD-A and enjoy the multichannel music they offer, why is it I want (at least it seems most posts state as such) to use those 6 RCA outs to the 6 RCA "ins" on my (not in my hands yet) 990? Is this because the digital output from a DVD-A player doesn't have the bandwidth or something? Or, is it because the 990 (and other pre/pros) can't decode DVD-A, and therefore, you must use the DVD deck's onboard decoder and thus use the analog out jacks? Or, is it that the DA converter in a DVD-A / SACD player is better than that inside the 990, so we want the player to decode it, not the 990? I'm confused...
Also, my Oppo doesn't "do" SACD. Not that I own a single DVD-A or SACD (yet), if I were to get a deck that did both DVD-A and SACD, I'd only be able to hook one of those players up to the 990's 5.1 analog RCA input jacks at a time, right? I guess that's obvious...
And one last question: My Oppo DVD player has 6 RCA output jacks for the 5.1 signals --- 2 x front, 2 x surround, 1 x center and 1 x sub, (plus 2 x "mixed" jacks which I assume is only used with an old pre/pro that only does the old DPL, such my current pre/pro Adcom GTP600...and, point of information, those are the only audio-out RCA jacks I'm currently using to listen to a DVD in DPL...my pre/pro doesn't even have digital inputs). Yet, I notice the 990 accomodates a 7.1 analog input, as it has 8 RCA input jacks. I assume then that some DVD-A and SACD decks have 7.1 analog out RCA jacks (8 total) as well? So, if I use my Oppo deck to play a DVD-A disk, would I be "missing" the full soundtrack as I'd only "output" 5.1 as I only have 6 audio-out RCA jacks? Or, would the 990 turn the 5.1 analog input into a 7.1 "sounding" signal (by some magic DSP stuff) and I wouldn't notice the difference?

Thanks in advance.