Marantz SR6007 receiver question

I am about to pick up my new receiver. I have upgraded from a Marantz SR5001 to the SR6007.

I only have 5.1speakers and will be hooking up the blu-ray player to the Marantz via hdmi.

When I watch movies with 7.1 audio, does the receiver add the surround back effects in the surround speakers mix or do I lose out on those channels?

Right now I can't watch movies in the lossless format cause the SR5001 can't process 7.1 lossless audio. Only up to 5.1. Don't ask me why. No one knows. So when i get movies with 7.1(most are nowdays) I have to watch the DD or DTS version.

Thanks in advance.

KEF Q50 mains, M&K center, Boston Acoustics surround, Marantz SR6007 pre, Emotiva UPA-700, Pioneer DV-46AV, Samsung BD-j7500, Sunfire HRS12 subwoofer