I liked the S-Types quite a bit, but I wouldn't try to go with a huge sail on an S-Type.
It sounds like you are asking if an 8.5 m2 rig will work on the S-Type 126.... right?
If so, I think you might be disappointed.
The S-Types were a pretty slalomy board, not real early to plane, and a bit of work to
get planing in marginal conditions.
When powered up, the S-Type was very good. Fast, a little technical (when compared with the same size Carve) to jibe, lots of "pop" for chop hopping and light jumping (better than the Carves in this respect), but you have to be able to get planing pretty fast before all these "features" kick in.
I cannot report first hand on the S-Type 126 with an 8.5 as I never tried it. I used the S-Type 126 mostly with 6.5-7.5 Retros and Huckers.
In 3 Bft (7-10 knots) windspeeds with an 8.5, you would have a hard time getting planing.
In 4 Bft windspeeds (11-16 knots) you'll probably have a hard time getting going until the wind gets to around 12 or 13 knots.
Remember, the S-Type is pretty much the opposite of your F-Type......much narrower in the tail, not an early planing design at all.
Hope this helps,