think of RMS as an average. On average, it puts out a continuous X amount of watts.
As for tweeters and cheap, think again. If you want to keep the blaupunkts, I know they also make a cheap(er) tweet. I think runs something like 45.
What I would do is upgrade your 5.25 kicks to a component setup. The 3.5s in the doors shouldn't be hooked up with the 4ch HU anyway. Infinity makes good stuff, as does mb quart.
<span style='color:gray'><span style='font-family:Courier'>1995 e36 3 Series RIP
1999 e46 3 Series BURN IN HELL
2000 MR-S Roadster= Current</span></span>