Been doing some research and came across this thread, which contains a lot of good information on exhausts for the S5. I'm posting this here mostly so that I know where to find it when I need to check it out again.
http://www.a5oc.com/forums/s5-performance-mods/19285-exhausts-apr-stasis-awe.html
From what I gathered from that thread, the AWE Touring is probably what would suit me best: sounds good (there's a vid on page 3 of that thread, I think), but, perhaps more importantly, no to little drone. Since my S5 will be daily driven, I'm concerned about drone in lower RPMs.