My speakers are really new (and so am I to this board
), so YMMV.
I'm using a Mythos 8 for my center channel, and I have tested it out with both movies and multi-channel music (Jazz and R & B mostly), while driving it with a Pioneer Elite Receiver (120 WPC)--crossover was 80 Hz using DD 5.1.
For movies, I find the center channel dialogue very clear and natural sounding, at both normal and at louder than comfortable volumes. The sound was detailed and various voices were distinct from the other sounds. This was even true in the very busy, loud action sequences in Chapter 1 of LOR:FOTR. Never sounded muddy to me--easy to understand without trying.
I also find the speaker quite musical--it tends towards the "less warm" side of the speaker spectrum, but makes up for it in a really crisp and dimensional midbass and high end. I cranked it up higher than comfortable, and it didn't sound strained or flat. Singing voices and piano sounded natural, although tending towards the brighter side of things, albeit not "tinny" or harsh.
I have not tested it with television signals. I haven't yet played around with different crossovers. Just for fun, I put it in a DT Pro Monitor system and it surprisingly blended well with even these less expensive speakers.
When you go audition the Mythos 8, I would respectfully recommend listening to it with and without a sub. It definately needs a quality sub to make it really shine, and listening to it only solo will give a biased impression of the speaker since it doesn't have a midbass bump. IMHO, a sub is necessary to give accurate picture of what it would sound like in a real world application, as that is the way it was purposely designed by DT.
To answer your other question: I decided to go with the 8 because its set of drivers match my L/R Mythos Ones. I also went with Mythos 8's for my rear surrounds for the same reason (I have not hooked these up yet). The aluminum finish 8's are also available at a really good price right now.
As I alluded to in the first sentence, my experience pales in comparison with other more veteran users on this board, so I'd be interested in their thoughts. I'm also admittedly biased since I just got the speaker, so others may have a more objective opinion. (There is also a link to a professional review of the 8's in the first post of this thread).
PS: My favorite remark about this speaker came from my 10 year old as we were strolling through a local higher end electronics store: "Gee, Dad, your speakers sound a whole lot better than those"