It seems like whether to mount the speakers in the rear door should be the least of your worries the way things are. Boss is hardly considered a good head unit brand (or audio brand for that matter). Likewise, Sony Xplod and Pioneer coaxials are pretty much flea market quality. I can see why you don't get good sound with them. Get yourself a set of good component speakers. There is plenty. I'd recommend something at least on the same level with Polk Audio DB or MM, Massive Audio CK6, Image Dynamics CTX, or JL Audio C3 (as a bonus, the last one comes in a version for doors with oval speaker holes), etc Run a dedicated amplifier for the front mounted set. 60-90watts RMS should be enough in most cases, but try a good brand amplifier. Something on the level with say Polk, JBL, PPI, or Alpine. Avoid Boss, Dual, Jensen and the like, and I'd say also avoid Hifonics or MB Quart. One solid 4-channel should be enough to power fronts and rears. Put the supplied tweeters (supplied with the component set, not those "1000watt" tweeters) in the door sails using the tweeter pods from cars that come with mach tweeter.