The power rating is pretty much meaningless in this respect, it wouldn't be a factor in matching subs necessarily....and isn't very useful information except to tell you the capacity of the amp (depending on what particular basis is spec'd). Mismatching would be more about different designs, like sealed vs ported, extension (how low it goes), frequency response overall, and spl capability. It's easier to deal with identical subs, but you can do well enough to get by with mismatched subs to an extent. Keep in mind the weaker sub is a limiting factor. Audyssey in the 3700 has individual sub pre-outs in that they can be separately adjusted for level and delay, which can help, but they're eq'd together by Audyssey. I'd get another PB1000 later perhaps, might do just fine for now on its own.