Michigan was really great fun, thanks to the great team at UMichigan. We're currently planning to be at ACADIA 2014 in fall, so we could try to grab a coffee somewhere in California ;)
Regarding your question: Basically any KUKA will work with KUKA|prc, as long as it has got six axes. I believe the KRL code from PRC also works with the KUKA SCARA robots (http://www.kuka-robotics.com/res/sps/e6c77545-9030-49b1-93f5-4d17c92173aa_Spez_KR_10_scara_WP_en.pdf
) but we don't have a kinematic solver for them. Similarly, it works for the LWR with its 7 axis, but won't show the transformation of the seventh axis. We've worked with KRC1 to KRC4 controllers and never had any serious problems.
One thing to keep in mind regarding used robots: The older the robot the less positions it will be able to manage, i.e. high-density milling projects will quickly cause problems with older robots. But many really nice projects were done with used robots, e.g. the Red Bull Arch project with a KR150-2 series 2000 http://www.youtube.com/watch?v=nqV56S_iZCU