Mt current setup consists of a pair of 5.25" comps up front (pioneer, may as well spend money on something decent), with the tweeters dash mounted and a pair of Alpine 6x4s in the rear. The tweeters sit at 45 deg, so are aimed towards the driver/passenger. Gives an excellent sound stage in front of driver/passenger.
I cant see why you couldn't do that with the tweeters, although the issue would then be a lack of noise coming from behind you. I had a similar setup with just front speakers and a sub, the whole lot sounded a bit strange. Also i guess it depends what head unit you've got and what sounds are sent to the rear? You obviously want all the correct sounds in the right places or it'll mess up stuff.
Cant see there being any technical issues though.
On a side note.. anyone have any good ideas where I could fit in 1/2 small 6 / 8" subs? The bass from the 6x4s isnt exactly ideal!

