So, with the SMS-1 I now have a great deal of control over the crossover between my mains and my subwoofer -- much more so than I have on my receiver. The SMS-1 allows me to adjust crossover with more options, with additional slopes, etc.

Is there any reason I should use the LFE out on my reciever, when I can instead set my mains to 'Large' and have the SMS-1 cover the bass management?

The SMS-1's crossover works well for the sub's signal, but it doesn't really do much for you on the other five channels - as such, it is not really a good substitute for your receiver's bass management. That's why I have the low pass crossover on my SMS-1 disabled.

I am confused. I disabled my pre-pro crossover and am using the crossover in the SMS-1 because I feel it is more versatile. Is this incorrect? Don

The SMS-1's crossover is different than the one in your pre/pro. The subsonic filter (a high-pass filter that cuts off the extreme low end) and the low-pass crossover are both very adjustable, but they work with the subwoofer signal only. You can route the left and right channels through the SMS-1 on the way to your amp (assuming you have a separate power amplifier rather than a receiver with internal amplification), but they will have an 80Hz analog crossover applied to them. There is no adjustment available for that.

I'd generally recommend using the SMS-1 for bass management only if you were in a two-channel system with separate amplification (or a pre-out/mains-in option similar to what the RR2150 offers) and can't do bass management in the pre-amp. If you have a surround receiver or processor with bass management available for all channels, you're probably best off using that instead of the SMS-1's bass management becasue it is a more complete solution.