LFE + main and a small speaker setting makes the sub setting inconsequential. The small speaker setting overrides any sub settings and sends everything below the crossover to the sub.
I run my M80s at 60hz and sometimes 40hz, they can produce a good amount of bass but nowhere near what the sub does. Just to check out how much the M80s are capable of turn the sub setting to off in the receiver, which will default the mains to large and run the system without a sub. They should give you reasonable amounts of bass, just not anywhere near as powerfull as the sub will do.
