I've been toying with those setting lately. Right now I have surround setting set to LFE and the 2 channel playback to LFE+mains. I currently have the crossover on both at 80hz but I'm experimenting higher and lower crossover points to see which sounds better to me. A great song to test the sub out with between LFE and LFE+main is Eminem's killshot. May not be everyone's taste in music but it is a good soundtrack to experiment on your sub channel.

LFR1100
VP180HP
EP600
M3 In Ceiling x 4
M5OW
M2 - Atmos rears
ADA1500.5
M3 Outdoor Speakers
ADA 1000.8