I also instructed at VIR with my 95.5 S6 track car & left my
S4 at home.
I was also disappointed with the initial pedal feel & overall
modulation on the S4 brakes. After repeated discussions with
my local shop, Tyrolsport, they let me try out a prototype of
their S4 solid brake bushing kit. The squish at the top of the
pedal is gone & the modulation is much better. BTW, I have yet
to hear the cold braking squeal.