Is this a crazy idea.

Mjcmt, Let me save you here, People seem to be missing the real issue, the OPPO players Digital processor built in does not have the capability to mix the Center Voice on a DVD disc to the front Left and right, Yes an old 4 channel receiver as long as it has the 4 separate mono channel inputs could in fact allow you to get away with hearing the front L & R , rear L & R just fine, however you will have no Dialog, because you will need a fifth channel in this case to output the Center channel jack of the oppo to another amp and fifth speaker..

Only way around this is to use what is mentioned above, A newer Pro logic type receiver from about probably 1992 and up that has the capability to take a connection from the digital outs either Toslink or Coax from the oppo player and decode the 5.1 signal of a DVD down to "Phantom mode" which yes then eliminates the Center speaker all together and runs voice thru the L & R while still retaining the Rear Speaker surround effect channels.

I mean unless you use both the L & R channels on the OPPO and simply set the processor inside the Oppo for Stereo out Mix not 5.1 Mix you can get 4 Stereo channels, but of course this will not be true surround sound or Have the Bullets speeding between the Two rear speakers it will just be all information sent to all 4 channels. So in a nutshell no you can't use old Quadrophonic receivers just for the amps and get true surround sound without a processor capable of running a 4 Channel phantom mode, and I doubt any DVD players have ever been built with this function in it.

I have tested it out on my Oppo 981 and it does indeed down mix the center channel to the front l/r when down mix 5.1 is selected and center is set to off (you can set the sub to off also). You should be good to go. Unless I'm still missing something?

"Is Flamb suggesting that only active speakers are ideal for HT?............if so your crazy."

Yeah, no, I'm informed, and plenty experienced! (about 23 solid years around and/or in high end audio/video. But thanks. Infact, just run your statements and comments on active vs passive through any high end custom speaker designer, and see if he's crazy too! Let me know, I've spend time at at least 4 speaker designers plants or homes, and it's just all achedemic here.

Chadnliz, there's a HUGE difference between active and passive speakers, that goes beyond just having some amps in a cabinet (although it doesn't have to be that way to be "active"), vs your favorite, choice amp driving passives!!!! Yeah, HUGE DIFFERENCE! The difference in large is that the active speaker has the amplifier dirrectly coupled to the drivers (woofers/tweeters), for SUPERIOR CONTROL, DAMPING, AND RESPONSE FROM THE DRIVERS!...that's what!!!
A Passive system uses (unless it's using no crossover design, or minimal, like Druids, Old Sonus Faber, Triangle, similar) passive, "current limiting" resisters, coils, caps, whatever, which restict current flow, and thus the actual control the amp has on any given driver.

So, to answer the question, as to whether active speakers are superior to passive speakers--All things equal (same drivers, same cabinet, even same amps (minus a passive crossover network, substituting likely an "active electronic crossover", or minimalist cross-over design), an active speaker is superior, hands down, yes!!! Ofcourse, it likely needs to be designed that way to begin with, mostly.
I once heard a demo of a pair of passive NHT 1.5's vs pro active 1.5's, and the difference was not suttle! The actives stomped a mud hole in the passives, threw mud in it's face, and threw a soundstage that dewarfed the passives!!!
Yeah, I'm very much into higher efficiency actives, even modified horns, and other that offer superior transient response, dynamic transparency, and realism, you bet!
I've yeat to be blown away by ANY, even high end passive HT setup, even driven by the best amps money can buy!
The Avantgards play in this arena, but then they're 110+ db horn speakers, crossed over to active woofers!!

Geared4me, you are correct it seems, I called oppo on this, they say they can run a Phantom mode, however its just not called that I guess in the player.. very interesting..