Multi Channel Pre Amp

5.1 or 7.1?
For 5.1, there's the Mac C45 and the AudioResearch MP1 as current models.
For 7.1, there's the Parasound P7 currently.
There are more in both categories if you are willing to consider used equipment.

Kal

Kal listed two I would recommend. As far as enhancing the sound that should be done at the source. Are you using the Oppo with 6 channle analog out's to the pre amp?

Yes, Five analog outs from the Oppo to the Onkyo.The sub goes directly to the Onkyo. What do you thing about the Arcam AV9? Will it have a noticeble improvement over the Onkyo???

Hi Doug,
If an analog multichannel pre-amp will suit your needs, I recommend you check out either the Sony ta-p9000es or the Arcam C30 fitted with the optional multichannel module (note: the current model Arcam C31 does not have multichannel capability). The Sony can now be had used for around $500 and the Arcam at around $1,000 or so.

Both are now discontinued but are great-sounding pre-amps for both stereo and multichannel music.

Of course, neither of these units will decode surround from your other surround sources like cable box/DVR or video game console, but should be a noticable upgrade compared to your Onkyo AVR as pre-amp.. -jz