not advice using amp for rear speaker...
4 channel amp, 2 channel for front & 2channel bridge for subwoofer.

i guess cause it costs less if you want rear fills
i have a comp set a the rear power by amp
staging still not lost

this whole thing about rear speakers is because of soundstaging la..thats it...but that depends on how u tune ur rear speakers la... if ur rear speakers are loud and overpowers the front then of course ur staging will ciao. which is why i recommend people to connect direct to player so it wont overpower the front. if wanna connect the rear to the amp oso have to tune properly la like i just mentioned. those who totally remove the rear speakers has 2 things in mind most of the time. 1/ soundstaging 2/ budget.

i never said the rear speakers is a must. but if u kesian ur rear passengers then put in the rear speakers just for the rear fill. which is what i did. now the rear passengers oso can have a nice bbalanced listening instead of the woofer overpowering the front speakers. which is why i mentioned boom boom. besides... with rear fills it also gives a nice surround effect. and yes some songs has the surround effect. hence having the rear speakers is better...again its just a matter of how u tune it.. but i still believe that even with really good tuning the rear passengers will hear more boom boom than actual music as they are much closer to the woofer than the front speakers.

as for 2 way or 3 way. not many icers would recommend a 3 way if the ICE has a sub in it. especially the 6x9 as it screws up the bass big time. i myself would NEVER recommend 3ways if theres a sub in the setup.

comps and coaxials. most people would recommend comps as u get better sound seperation. positioning of the tweeters plays a big part in alot of SQ systems. which is why components are preferred. its just that most people put the on the dash to make life easier and dont have to fabricate the locations for the tweeters. coaxials are mainly used as rear fills most of the time. not many people use them for the front. and as far as i know there are NO ice kaki that uses them for the front. actually there arent many ice kakis that uses coaxials at all.