Thanks for the Mach RCU and tweeters you sold me a week or two ago. The Mach sounds great in my 2002 Taurus. It also works well with my PIE auxiliary input. I can't wait to find some time to install the tweeters. Since I have the SES it looks like the tweeter connectors aren't there but I'll just have to tap into the existing speaker's wires. I am also happy to see that my old sail cover and the new one with a tweeter inside have the exact same mounting foot print (all the holes line up).
The stock RCU is 12 watts total - 3 watts per channel. The MACH RCU is 80 watts total - 20 watts per channel. With the old RCU I would need to turn the volume up to half or higher on the highway with windows down; the volume that high caused a lot of distortion. Now, I normally go to 2 or 3 dots on the volume and its plenty loud with no distortion.
As for the tweeters, they help make the difference. They handle the highs and let the door speakers handle the lows. In my opinion, the MACH setup is a 200% improvement over stock.