Thiel CS 1.6 vs ProAc speakers vs ?

you say tomato, I say tomatoe - I prefer the ProAc's - more musical, better tonality and less 'high-fi' sounding.

You must audition to know which YOU prefer.

I think it really depends on what kind of sound print you dream of. None the less, proac is a bit laid back british speaker with very smooth treble and nice tonality, Thiel is a rather agressive speaker with lot of treble energy and with more bass slam, arguably at the expense of midrange. If you mostly hear classical music, my ticket would be the proac. If you like more rock music- maybe thiel is your speaker. But you really should audition in your system whether the treble of the thiel is not too much for you.

Given your system and tastes a set of Vandersteen Model 2Ce Signatures would be your best choice IMHO. See the recent threads on them for more details compared to Thiel, etc.
Good luck!
Michael