Chris, I was wondering the same thing before I bought my Autoexe springs. From what I gathered here on this forum, the Eibach springs are spec'd for a regualr FWD V6 3.0L Mazda6 sedan and hatchback. Members who have this application seem to like the results and their cars look fine.
Autoexe springs on the otherhand are from Japan and are spec'd specifically for the MS6 AWD. I was a little skepital until the box arrived and the label was written as "MS6 Aetnza" in Japanese.
If you read the threads for the Autoexe springs you will find some members are willing to spend the extra $ for an application specifically for the MS6, including myself.
I pretty sure the installation is a standard spring swap deal (air tools and a spring compressor for the fronts would help) but I cut my bumper stops in the rear by two notches to allow the OEM shock to go through its full compression since the car is lowered.
At any rate I'm sure I'll be going though shocks pretty fast because at this time there is nothing spec'd for the MS6 with a shorter shock body.