With regard to the timing problem, you're going to want to run those rear channels both about 10-20 ms behind (with greater delay than) everything else...otherwise, they can really separate your front stage and pull things to the back. If they run on a timing plane that's closer to you, it's to be expected that your front stage is screwed up by their presence...your ears are telling your mind that since the sound from the rear gets there first, then the music must be behind you. If you only can get delay on two channels, I'd seriously consider either delaying the rear only, or, if you're a nut for centered vocals, ditching the rear fill altogether. Consider looking up what people are doing with regard to filtering rear fill for frequency. I haven't done it, but I believe that all you need at the back is some midrange for ambiance (bandpass filter for lower voice frequencies only), along with a strong delay to take them completely out of the loop with regard to time-of-arrival location cues. Those PA's aren't gonna mesh well in any case, imho, with those Infinitis. With regard to your output problem, I'd give those pioneers a little more top end, try 100 Hz, or even 120, and set up your front stage accordingly. You're kind of in a bit of a bind when it comes to the 80-200 Hz range with those little 5.25's in the front...Look to tighten up your install up front, make sure they are securely mounted and that your doors are deadened well.
If you're looking to do any equipment additions/replacements on the cheap, I'd find a pair of decent, dedicated midranges and couple them with a set of 8" midbasses up front, and can the "rear fill" altogether...or if you wanna keep the rear fill, put those 5.25"s on duty in the back after you get something more in line with your goals for the front...in fact, if you wanna be really inexpensive about it, then just get the 8"s for the front, and let those infinities pull vocal and above duty only. The type of music you listen to, you're looking for that 100-300 Hz punch in the gut, and you're just not gonna get it with a set of 5.25" playing all the way down to 80Hz...it can be done, but I just haven't heard that size speaker do it without making sacrifices... (I have a hard enough time with my 6"s in this regard).