I could use the S8's as mains. In fact, at loud levels with subs, I prefered them over my old 212's.... I know that sounds crazy but I found the 212's pretty bright when they were really loud, the S8's don;t have that same brightness at all and I could stand them louder in my room than the 212's.
I've had this conversation a few times over PM's with a bunch of people, I did find the 212's bright at high volume, the same couldn't be said for my T8's or T12's, At the same volume, I never found them bright. The 212's even though they were a bit bright, still did IMO do everything better but I had to tame down the upper Freq's to my liking.
They do lack the fidelity of the 212's, thats for sure, it's a horrible comparison really, a small bookshelf vs a reference 3 way speaker.... that being said, IMO they still do very well!!
Blasting brown notes for 10 years and counting!