Since you're running a Double-Up with all 8s and 80s, versus the 60s, a single SYN 2 would seem to fit your application and be very cost effective. With a parallel stereo scheme and a 2-ohm load this would give you a symmetrical 175 watts to each of the four speakers. With the robust driver of the MB-8, power handling us a non-issue. And, with this particular combination the ability to differentiate on the electronic highpass would be less critical, if at all, as compared to the typical MB-8/Pro-60 Double-Up. At 700 total watts, this is just on the heels of the SYN 6 710 total watts.