MS-8 creates a single channel center signal. You can use the built-in amplifier to power it or use a free channel on a full range amplifier.
How do you decide on an amplifier if you want more power? This may not be the best way to do it, but if you have 2 channels free, you don't have to bridge them to create a mono channel. A reason to not do this is if it's far more power than your center speaker can handle, such as 250W RMS bridged for a 30W RMS coaxial speaker. For example, I was using 5 channels of a Clarion XC6610, which is rated at 85W x 6 at 4 ohms. 2 channels bridge to 250W RMS, and I didn't want that much power going to my 2-way 4" components that composed my center channel. For those of you who know what you're doing in regards to headroom, disregard this paragraph.
You guys probably know I have a lot of experience with CDT speakers. I've been selling them for almost 5 years and until recently I never went without CDT speakers in my vehicle. I had the CS-020X Center Stage kit many moons ago, but not with MS-8. That kit requires a fairly large flat surface to mount the pods, and a lot of dashes in late model vehicles either don't have that flat space or the pods will look really, really out of place. I've talked to and e-mailed a LOT of people about center channels, and I've not sold a 2" mid/tweeter to any of them for that purpose. It's not because it won't work, it may be that it will sound great. I've ran ES-02 without a small tweeter and I felt the top end was too mellow. It was fine at low volume but it quickly got overwhelmed when I wanted the system to get loud. I think it's fair to assume most of you guys want your system to play loud, and you want to hear everything in the music.
To continue...MS-8 with Logic 7 puts a LOT of information into that center channel. The reason some have suggested to use the same woofer and tweeter for your center as your front left and right speakers is so you can try to maintain the same timbre and impact. I wouldn't expect any of you to chop up your dash for a 6.5" woofer and a tweeter, but if you could do it and do it RIGHT that could be epic. When I decided I had to try a center channel with MS-8 I first used CDT's 6-1/4" shallow CL-6SL mid-woofer and a TW-25 1" silk tweeter. The baffle was a big flaw in the project as I used 1/8" ABS and it was all hacked together. Don't do that. It did convince me that I was on the right track, as I later settled on ES-04 and HD-1A/BL with a 2-way passive crossover. I built a sealed enclosure for the midrange and cut a big hold in the dash pad to try to sink the enclosure down as far as possible. This was bolted to the dash pad. When I had it wired for 85W RMS the crossover was 100 Hz @ 24 dB/octave. When it was wired at 250W RMS, the same as the front left and right midbass woofers, I crossed it at 200 Hz, 24 dB/octave. It kicked ***.