All sifus and pros..seriously need advice here.

I'm driving Myvi and recently just started to upgrade my ICE, here's my system:

Kenwood 4036U CD player
Kenwood 4" 2-way speakers (forgot wad model)
Kenwood P603 6.5" component system

I mounted all the speakers to myvi's original position, whereby the 4" speakers and tweeters on dashboard, and 6.5" midbass at rear door panel. My problem is that the sound from the front are loud and clear, but at the rear, the sound is so low (almost like no sound) . So i went to ask around, and my friends said that I should not split the component system, instead mount the midbass and tweeter at rear dashboard. This way I can get sound from rear and deep bass . All sifus, pls advice wad I should do.

Secondly, I've saved enough money to get an entry level 4-channel amp for my speakers. Budget around RM500 (hopefully enough) . Any brand and shop to recommend? I'm staying in Subang Jaya. Still saving money for 2-channel amp and woofer, budget around RM800...maybe can advice too? Thanks.

Better fix the 6.5" mid at front door...

already done moving my midbass d. Since front got 4" d, so all move to my rear dashboard panel. Then today add another subwoofer and 2 channel amp, my ICE:

Kenwood MP4036U HU
Kenwood P605ie 6.5" Component set
American Sound CS50.2 2x amp
Lightning Audio 12" Sub

The SQ really is great. Satisfied.. hehe. Saving money for 4x amp right now..