Jeff
I have Martin Logan mains and center, Spica TC50 side & rear and 2 LFM-1 subs. I set my mains to large everything else to small and subs to LFE. I have not notices any problems. With this setup the bass can be suttle to shake everything off the walls, it depends what you want. If I use the 990 for 2-channel music I use bypass which only uses the mains (I believe). The bass has never been a problem in having it over powering with any of the settings you are asking about. Even with all of the problems some people seem to be having. I would not hesitate to purchase a 990. I don't think you will be unhappy. Give it a try the worst that happens is you send it back at 30 day. But I doubt you will.