I haven't done much testing with the M3 so far but it does what I need (mainly 3 sources) with full file description quite well. The integration between keypad and M3 is really really good imo, I can't picture how software products like casatools would be able to compete in the same scenario.
Right now I'm using 5 of the 6 sources (3 for the M3, 2 for the T2) and the last one is sort of like an all-purpose utility source in. Sometimes I connect my laptop as a source, othertimes my TV, etc...
How do you change tracks during playback with casatools? can you use the keypad? or do you have to go to your computer that has casatools and change it there? if it's the latter why would you even bother? I mean you can just use winamp, wm player, or any other mp3 player and broadcast it as a single source.
A lot of people on this board won't like what I'm going to say, but I purchased my in ceiling gear from outdoorspeakerdepot.com and had no issues whatsoever. Their prices are cheap, and shipment & feedback was impressive (within 1 hour turn around time). Some guys here say their products are cheap but I look at the items and it's all brand name stuff. I bought 8" Pheonix Gold ATC8's at $85 a pair, compared to Radio Shack $220 for the same. These speakers are going to be used as background speakers not home theater and they are excellent in their function so I see no problems in saving some money.
Oh and one more opinion (you prolly heard enough outta me ;-) ) go with 8" if you can - I didn't like the sound of the smaller 6" speakers at all.