at least the PPI amp has a 10x switch on ch1&2 and bandpass on ch3&4 so it's active capable. that's a very nice feature. you could run the comp sets active, but you'd lose any ability to fade to front. if you're the type of person who always has fader in the center, active is something to consider. tweeters on channels 1&2 and woofers on channels 3&4.
to use the amp normally - front on ch1&2 and rear on ch3&4 you can adjust the HPF on the PPI amp by ear to remove just enough bass to protect them, but keep enough so you get midbass.