With a 40Hz crossover, your M80s are already playing almost as low as they handle strongly. If anything, rather than having them and the EP800 both playing low bass by setting LFE+Main, stay with LFE, but give your excellent sub more bass to work with by raising the M80 crossover to 60 or even 80Hz.
No, Audyssey didn't set the sub low-pass control to 120Hz. If you set that all the way up to 150Hz(as you should), it stays there.
If you really want to set the sub level a little higher than the calibrated level, set the volume control on the back of the sub just slightly higher.
