I think the Outlaw Audio SS receivers have always had pre-outs for all channels.
yeah you should be able to simply insert something like a used quality DD/DTS pre-pro (that has a multi-channel input/bypass) into your Mac's multi-ch input(should have one). The, you can simply connect that to the Mac, digital connection from your sat box to that pre-pro, and out to your MAC. Any SACD/DVDA connections can be done through the AV-pre, which will go out to the MAC.
Then, when you need 2 channel sources, via analog, you can simpy run the Mac. Easy enough...
Maril555, that is indeed a very nice pre-amp. I have the MX135 which is built on that chassis as a base plus the processing. I would try for the MSD4 if you can find one they would work together nicely. Check with audioclassics.com,I bought one there a few years ago used and it was in excellent shape.