Hey I'm also a big Sony fan... Just don't have cash for decent sound atm...
But ja here is my setup: Sony GT616, 12" Sony xplode sub in custom enclosure, custom back board with 6x9's and still got the stock front speakers.
I built myself a new backboard because I didn't want to cut my original one, but due to that the backboard is now very heavy. so i didn't hook it up to the boot lid, I was afraid it'll rip out that little plastic hakkies..
But non the less the car sound good I just want to replace my front spreakers with some mids.
Alfy the radio you're looking at is very nice, I-pod connectivity and so on.
And ja normally 7x10 was spacers in thus ppl cut the hole the size of a 6x9 but just check to make sure..
ok and on the whole split/coaxial/mid thing:
Splits: This is a set of speakers containing a crossover a tweeter and a midrange driver.
The crossover is there to take out the low and midbass to the tweeters and only give midbass to the mids(4-6"round speakers).
So the tweeter give the clear hi piched sounds and the mids the normal midrange sounds.
It works best If you have a sub for the low bass, and another set splits in the rear as well, though you will need an amp that can run both split systems and the sub...
Mids: like i just said it's just a standard set of 4-6" speakers no built in tweeter.
Coaxial(ok here i might be wrong but): This is a round speaker with a built in tweeter so the tweeter is on top of the speaker.
So if you have the cash go for 2x sony splits, sony 12" or 2x10" subs and a sony or targa amp. IMO.