MacD,
I have experimented with bi-amp the 120s and the 500MB and was disappointed. I did not use a x'over. I used the balanced and unbal outputs on my cary slp-05. The 120s did not provide me with the sparkle that I was looking for. An upgrade to the BEAST - 28b-sst may provide you with better results. The resale on the 120s is not that great either.
I have experimented with bi-amp the 120s and the 500MB and was disappointed. I did not use a x'over. I used the balanced and unbal outputs on my cary slp-05. The 120s did not provide me with the sparkle that I was looking for. An upgrade to the BEAST - 28b-sst may provide you with better results. The resale on the 120s is not that great either.