Check out Outlaw's SMS-1 Guide - it may help you understand how it could benefit you, whatever sub you have. Basically, it is a way to help resolve problems with room acoustics that no amount of extra subwoofer power could fix.

I would like to see an explanation of why the 7700 has better sound quality than the 7200.

They're likely referring to the balanced design. From what I've seen here on the forum, that's really the only difference between the old 770 (from which the 7200 seems to be directly descended) and the 7700.

The LFM-1 Plus has arrived . Exact same cabinet dimensions and weight as the LFM-1, but 25W of extra amp power and the ability to drop down to 18Hz at -2dB. It's also on the order page now.

Yeah, I was just taking a look at that, but there is still no Combo for the LFM-1Plus with the 990/7125, 990/7700, 990,7500.
I'd think it would just be $100 more.

Wow! Someone at Outlaw must of been listening!
There are more combo's listed.
http://www.outlawaudio.com/mofcart/combos.html