Is this a crazy idea.

It depends on what 4-channel matrix circuits the quad receiver can do. What kind of receiver is it?

I think it would be better to use an analog Dolby ProLogic processor set to phantom mode (it sends the center channel mix equally to the two front speakers). But you may be able to achieve similar results with the receiver depending on what matrices it can do and how much control it offers in channel balance and time delay.

If it doesn't quite do it for you, I have a Shure Dolby ProLogic outboard unit. It was state of the art in 1994 and sold for $1000 back then, but I would of course let it go for *MUCH* cheaper today.

Problem: It will never be as dynamic and 3 dimmensional if you're NOT USING an outboard DD/DTS pre/pro! Processing DD/DTS movies in your dvd player, and passing the info out analog to a preamp (which is what you're doing), never works as well, overall! It's just to flat sounding, and not enough snap and punch to the sound. That's my findings.
Basically, I never encourage trying to re-invent the wheel here. But audiophiles just keep on cutting corners with HT systems, trying full range passive setups all around, bypassing processors, avoiding bass managment and subwoofers all together--and they always tend to think they're onto some "hot-ticket" approach!
Yeah, no.
Anyway, you could tinker, but I think you'll find what I'm saying. good luck

you are nuts...but you've got 4 great speakers

With respect to Flrnlamb, my "double stereo" in no way is "flat, without snap or punch". Front is a pair of heavily modded Spica TC50's. Rear is modded JBL L-166's. Cables are Cardas Golden Cross interconnects, Cardas Hexlink 5c speaker cables to Spicas, Toshiba DVD, Rega amps, Tice block filtering, Cardas Golden Power Cables. It kicks butt and is WAY better HI-FI than store home theatre set ups I've heard, minus of course all the "3D" stuff.
So to MJCMT I say, you go boy!

I don't think it will work. If you use 4 of 5 analog outputs from your Oppo DVD player, you will have the DVD player set to 5.1 or Dolby Digital output in order to get any sound from the L&R rear/surround output jacks. This will also cause the discrete center channel information to go to the center channel output, which you don't have connected to anything. You will be missing at least one 5th of the discrete information (all of the center channel content) from your DVDs.

I'm guessing that in order to use anything less than 5 channels of output from you Oppo, you will have to set the output mode to PCM or stereo. Then, you will likely only get output from the L&R front analog outputs.