To get the most out of the Pro60's, you need to feed them in the neighborhood of 200 watts RMS each. The most economical way to do this is to go with a 4 chnl amp bridged into 2 chnl mode. At a minimum, 150 watts rms. A 2 chnl amp is the ideal amp, but I think one of comparable output would cost more.
The XS650 is a hi-performance, hi-output speaker. It really shines with some power behind it. I would want 75W RMS to each at a minimum. For just 2 pair, you could go with a 4 chnl with each having its own chnl, or a 2chnl running @ 2 ohm p/chnl. Even powered and tuned the same, there is a difference in sound between the 650 and the 65 series Wet Sounds in-boat. Both sound great, but if you get a chance to demo each, it will be worth it. I've listened to the 650's powered only by the head-unit and just finished an install with 65's driven by a Syn-4 @ 100W RMS. So both sound great, just a little different. If your budget (and mounting depth) will allow for the XS-650, then give them some solid power as well.