Two sub outputs are a convenient way to connect two subs - rather than using the splitter that would otherwise be required. There are a lot of people running two subs, and the second sub output is handy for them. Two subs are useful for achieving higher SPL's (especially in larger spaces) and smoothing out room nulls. I've always just run one sub. Space limitations would start to creep in on me if I tried to add a second, not to mention the fact that my wife would probably prefer not to add any more boxes to the room. Since I haven't ever heard the LFM-2, I can't say how well a pair of them would compare to a lone LFM-1. I can say that I've been very pleased with my single LFM-1 in my 17'x23'x8' space.