I haven't heard them but id roll with those 6x9 components over some coax for sure. dedicated 6x9 midbass and separate tweeter should sound real nice. Plenty of cone area for some nice solid midbass. A higher tweeter will help bring the soundstage up as well. Plus if you get more serious down the road u can easily ditch the passive x-overs and run them active.
Although, I think a set in the back is overkill. Rear fill should be just that...filler or ambience. When ur at a concert, how much music comes from behind you, if youre looking at the stage? I think that's where you should find a decent set of coax 6x9s.
Ive got mixed emotions about hifonix. I think theyre a pretty good budget amp that will do close if not right at rated power. Ive seen guys beat on em for 2 years with no issues and others swap out a 100x2 4 different times for random manufacturer issues. id def buy one from a certified dealer with warranty if you go that route.
As for the sub.....That's not the one you can buy at wal-mart is it? lol