2 channel music in direct mode will allow your sub to work with the speakers and no crossovers. LFE+Main means the LFE signal in DVDs will be sent to the main speakers as well as the sub, this option may help poor room dynamics and spread out the LFE providing your mains are up to the task. When the mains are set to small and a cross over point is made the receiver starts to send anything below that point to the sub and frees up the load on the receivers amp and the speakers are free to articulate the area of sound they do better at. For M60 - 80 the crossover is usually set around 50-80hz depending on the room and how the listener likes it.


Jason
M80 v2
VP160 v3
QS8 v2
PB13 Ultra
Denon 3808
Samsung 85" Q70