Sl60 will give you very warm, smooth and balance performance. Boston really famous with their smooth sound and good vocal reproduction.
If you are a first timer in ice and planning to replace your stock HU, Boston is a good choice. Go and try polygrass and dos, both are good speakers at reasonable price.
Regarding sx60, it is an upgrade version of s60 with warmer sound, the difference in the midrange speaker, but try to go for sl60 if our budget allow. I used s60, very asy to drive, decent sound quality. I upgraded my Boston s60 to mb quart premium, I still think that Boston better in handling vocal albeit a bit weak in midbass.

Btw, anyone interest with my s60? Lol

At KF they installed those speakers on wooden frame, will sound differ from the sound when you install it in car.

I also hope to get audison, saving for it.. lol

Maybe can consider my two 2 channel amp
http://forum.lowyat.net/index.php?showtopic=2231946&hl=

Very powerful