Sounds like the combo transmitter/receiver is a pair. So if it is more power you're after, I'd say just get a new package that does the same thing with a larger amp, however if you look at any of the ones that are higher power, they're not cheap and there are not many out there. SVS offers one that 150x2 but is not surprisingly, quite pricey.
Alternatively, and maybe the easier choice, is a set that is only transmitter/receiver with whatever amp you choose.