Dolby EX should be giving you7.1 sound if there's a discrete track to decode. PLIIX should be forcing a signal to the rear speakers by splitting it off of the surround tracks. DTS Neo6 will also give you a digitally contrived rear channel sgnal.
None of these can be applied to the 5.1 analog signal from the Toshiba. I don't believe the 990 applies any processing to the 7.1 analog input except bass management.
I believe that Dolby EX will only work with the digital inputs. PLIIX and DTS Neo6 should work with either Digital or 2 channel analog.
When you say is there "any" way to get rear channel sound from thr 5.1 inputs, yes there is.
The HD-A3 doesn't
have a multichannel analog output. Skitlboy is using an optical digital connection because that is the only choice available to him, and when the HD-A3 decodes a DD+ or TrueHD track it re-encodes it as Dolby Digital 5.1 at the highest bitrate supported by Dolby Digital. He can use Dobly EX or Pro Logic IIx to expand that Dolby 5.1 track.
Okay it looks like 7.1 is out.
How about 5.1 surround through a 7.1 system if the DVD output is only 5.1? Does it make sense to feed the right surround signal from the 990 through the right middle and rear surround speakers and the left surround signal through the middle and rear speakers? Would a Y-connector make sense for this? I bought the extra speakers and amp because I had the money at the time and I would hate to have them just sit there.
Thanks to all for your help.
If you are using Pro Logic IIx, I'm unclear on why you aren't getting 7.1 sound already. There's absolutely no reason to use y-splitters or other workarounds. Connect the seven pre-amp outputs to seven amp channels, and then in turn to seven speakers. Enable the 990's surround back speakers. Once that's done, when you apply Pro Logic IIx to a Dolby 5.1 source, you will get 7.1 output.