The PLX2s are very nice amplifiers. If it's the PLX2s vs the Crown XTi's i would give the slight edge to the PLX's, here's why
1.) The PLX line has an extremely good track record. They have been industry workhorses, with very very little problem. The XTi is relatively new and has yet to prove itself.
2.) The XTi's DSP is a cool looking, but probably not very useful for most of us. The PLX2's also have cool switchable filters built in the back, that will act as a crossover if you like. However, I do like the built in hard-limiter of the Crown XTi.
3.) XTi is kinda like crown's low level amp. While the PLX is QSC's mid level amp. This is apparent in the country of origin, China vs USA made. This may or may not matter to you.
Power draw betweent the two amps are similiar. Keep in mind that the XTi doesn't have any of the awesome technology that higher grade Crown amps have in them. Don't let the name fool ya! The XTi's don't have i-class/bca technology, nor does it have Power factor correction (PFC)