Hello Jeff,
I looked up the manual for PS Audio BHK600 – see attached.
It says that it is good down to 2 Ohms for musical transients …
I am surprised that they responded to Keith that they could not power the Sound Lab, except that there is a very high likelihood that they do not know how easy the Sound Lab is to drive (since newer versions after 2006-ish, and especially after 2012)
There is, however, one possibility that they have a overly-sensitive protection circuit – and because Sound Lab’s are so fast to respond to music signal, they demand the fastest response from amplifiers – some amps see this as a ‘threat’ and go into protection (turn off for a few seconds and turn back on usually)
Let me know if you have any other questions – I actually use a 60W David Berning amp and it performs amazingly and I can get 90-95db response from Sound lab’s largest panels in a large room…And Benchmark AHB2 never ever misses a beat.