Dude, you haven't found the good threads yet.
If you get the Focal components, there's no reason to get OEM tweeters. I personally can't stand the Focals, am on record saying they are bright and forward and fatiguing to listen to.
The CleanSweep does one thing and one thing only - "normalize" the OEM speaker signal to be close to flat. It isn't a crossover, or a user-adjustable EQ, or an acoustical-optimizing-auto-adjusting EQ.
The MS-8 is all of those things, and a low-power amp suitable for rears and center speakers (and sometimes fronts in base-bones upgrades).
Technic, if I understand correctly, was suggesting that you get just an MS-8 and use its 20 watts per channel to power the OEM mids, some OEM tweeters you'd need to get, and try powering the underseat speakers.
I personally think that that won't work on the underseat speakers at all (it's been tried) and you will need to get better underseat speakers (SWS-8 are one that works) and get an amp for them.
So one way to do that is to get an MS-8, a small 2-channel amp, OEM tweeters, and SWS-8 woofers.
That works pretty well. We sell all that but the OEM tweeters.
We would normally do it with Zapco amplification (we preadjust it) and their speaker level interface, and Rainbow speakers in front and underseat SWS-8 woofers to start. I think that sounds better than the system above (and costs more).
But I don't remember your budget. What is your target?
If you'd like more info, shoot me a PM or email off our website, thanks.
Musicar Northwest Portland OR musicarnw.com
High-performance audio for BMWs