The PB1000's speaker outs are passthroughs I think. They only supply the power passed from the speaker-level ins, and they may be crossed over with a high pass filter at 80Hz anyway.
You could hook them up to your receiver, but they'd play full range unless your receiver has an amplified sub out. Better to get a dedicated amp, or at least find a cheap receiver on Craigslist you can pass the LFE from your main receiver into. I'd say the SMSL tripath amp I've been pushing in that Australian bookshelf guy's thread would probably work pretty well.