If the frequency response is indeed accurate and is within +/- 3db, I would set the xover at that number or the one setting higher than that number (for example, if you can't set it to 65hz, set it to 70, or 80, whatever the next highest setting is). The higher you set your front crossover, the more front left/right bass will be sent to the sub instead. The only thing the LFE trim will do is turn up the sub, it won't send more frequency range to the sub.
As for surround settings, nobody can tell you what you will like best, you will have to try them out and listen, see what works for you. It's subjective, just like speakers themselves are; different people like different sounds, therefore, nobody can tell you "what speakers are better" than others or "which surround mode is better". That said, just because something already sounds good doesn't mean something else won't sound better, if you like "MultiEQ" you should still try out the other settings, because you may like something else better (though it's doubtful, Audyessy is very good).
I'm sure if any of this info isn't correct batpig or jd will let you know, and they can fill you in on the details I can't help you with as well. I don't own one of these receivers, I'm just speaking from my general knowledge of receivers. batpig and jdsmoothie are godsends, at least in this thread, if not this forum. They seem to spend almost all day answering people's questions and they don't tire of it, even when people ask the same questions every day (like I did when I joined this thread).