For HT purposes, I would set your sub's volume level all the way up at the receiver, then control its volume by hand. Set the sub cross over (on your receiver) at something like 80hz. Turn the crossover knob all the way up on your sub. Set all speakers to small (though I usually leave my M60s at large).

That was the advice given to me here and I found it to be good.

Then, for music, you may have to switch it all back again to get the sub to behave itself.