I'm not really the ideal person to answer this Matt, but I've got a loose formula that may help;
The 17" Monza's fit over the R32 front + rear setup, so, how much bigger than the R32 setup is the S3 brake setup or what are the size differences?
From that, you should be able to work it out but I'd hazard a loose guess that they'll be okay?...
I've seen on R32OC in the past 2 lads with different BK's and both ran Charleston wheels. Whether the BK's were bigger or not, I can't really remember but their .:R's were quite seriously engine modded.
Hopefully someone more experienced will give you a more accurate answer however.