I'd run 2 amps, 1 x 4ch for speakers&tweeters(i imagine these are splits?) and then another 2 ch amp for the subs, make sure the amps can handle the speakers peak load, should work fine
I have splits up front and 2 or 3 ways in the rear doors and a single 12inch sub in my vx have 1 4 channel amp for the speakers and a mono block amp for the sub does the job quiet well