to be honest, wasn't really in any bars, dont remember too many near the train station...think there is an area by the river that caters more for that , taxi to get there (sorry cant remember the name, begins with an S anyway!
(i dont drink and by time we got there on the friday, we checked into hotel, went for something to eat, friend got some booze for the room, then we went to cocoon, bought some **** pills off some italians:x left cocoon to try robert johnson, then got knockback, so just called it a night 5am-ish...train through to time warp on the saturday (which is free with the timewarp ticket)
if you went in small groups, and early enough you might get into robert johnson., but i get the feeling its pretty much germans only that friday and they dont want techno tourists in the place..... cocoon is now closed, but its been re-opened under the name moon...by the looks of it the music policy has shifted quite a bit, but i thuink your group would get in no probs...perhaps an option, cracking club, and worth seeing..(im taking they haven't re-modelled it too much inside)
http://www.moon13.de/index.php?s=eventoverview
im not going, but my friend who i went with last year is, not sure of her plans, will see her in a couple weeks and will ask her itinerary)
my lasting advice, dont buy pills off any italians (at time warp either)