Speaker question.

I've made a few threads here before and alot of you seemed to be very helpful, so I decided to come back with another question.

I've talked about getting the CDT Ef-61 speakers for my doors, but I haven't got a chance to get them yet, but here in a week or 2 I'll be able to get them along with the amp. My question is, will they fit in any 6.5" slot? I drive a '97 Saturn SC1 and I wasn't sure if they were too big for my type of doors. The height wise. Or will any 6.5" speaker fit in any 6.5" slot? Just wondering.

My other question is, after getting those, will there be a need for a rear fill? This is my 3rd system and I've always had rear fill, and I think it sounds better with sound from the rear. But I've never own anything "good" like the CDT's. Should I get rears or would the CDT's put out enough sound? IF I get those CDT's, and I still feel like I need a rear fill, what would be a good set of 6.5" (my rears are 6 1/2 too) that would put out some decent sound? I don't want to spend over $150 on rear speakers, but something worth the money & clean sound.

So that brings me to my last question. If I get the rears, what would be a good 4-channel amp to power the CDT's and the rears? Or should I wire the rears off the deck? I don't really want to, but if I have to then I will. And what specs should I look for on a 4-channel amp to power the CDT's AND the rears?

I got all my equipment and it sounds great for my liking, I'm just missing my front/rear speakers to give it a cleaner/better sound.

Thanks for the help in advance.

also forgot to add, right now i got some cheap pioneer speakers (front and rear) that I got from wal*mart last year. so basically anything you guys mention for my rears will sound ALOT better than those.

i just need some tips.

My opinion is that  you use only speakers for rear fill that would also sound "good" as the front main speakers.  For example, using the previous front speakers or like quality when you upgrade to better mains.  But if your current speakers are from Wal Mart, you can forget about that idea!

I  had two sets of Pioneer 6X8s as replacements for the OEM speakers in my personal car and replaced the mains with CDT components.  I left the rears in place, attenuated them a bit more than the way I had it before the switch, and the overall sound is very good.  I've listened to a few different models of Pioneer coaxials and found that the ones I have sound good but the others were lacking (guess I got lucky that day on Ebay...).  In your case, use a pair for the rear that you appreciate for their quality in and of themselves.

Use any good quality 4 channel amplifier for the two sets.  You can adjust freq response and gain for each pair.  As opposed to what glacious above said about getting a "surround sound" type of effect, I believe that the best use of rear speakers is to have them attenuated to such a degree that even when sitting in the rear seat (of a common sedan) that the front main speakers are still heard as the primary source of the music.  In the front seat, the rears should just be loud enough to bring the music up in the front to windshield level.  That provides the best soundstage.  In my instance, the fronts get up to 65 watts where the rears are probably only getting 20 or 25 watts by use of attenuation.  That's just a guess, of course, as it was adjusted by ear.