A 5.1 mix is surely capable of having LFE in the mains or any other channel. It's ip to an individual processor as to where it actually goes. Most home setups are best diverting all frequencies below 80hz to the sub per home THX recommendations. I have large Klipsch RF-62 towers as my mains that can get pretty low but still do better when only handling things above 80hz with all frequencies below sent to the dual subs. The sound is more robust and menacing. For music only though, I run the mains with no processing at all or bass redirection for optimal results.

Experiment with your setups and see which sounds best. Your ears are the final check of any calibration. Don't always trust the numbers.