Yo, FT.
There is another posted response on this board from a couple of days ago about creating an LFE track from the stereo mix...search for that for my detailed response.
With regard to the Surrounds, here is an excellent way to create some surround fill from the L/R but with some filtering - you want to avoid Dialogue in the Surrounds for a more enjoyable experience.
1) If you have isolated Music tracks feeding your L/R mix, bus them to a new stereo pair
2) add to the bus a STUDIO REVERB / ROOM AMBIENCE 1 (set the mix to 100%, 0% dry)
3) add either a Paramentric EQ or a Scientific EQ to perform a LOW-PASS filter with a nice 24dB/gain RollOff set at around 8kHz (w Scientific LowPass/8kHz/Order=3)
If you don't have an isolated Music source, consider using a longer reverb set at a lower level with a stringer filtering - the goal is to fill the space with sound but not distract the listener from the front channels which Dx (dialogue) tends to do.
Cheers,
-CS