I preferred both my Stepdance and SR71A single ended to SR71B single ended. I didn't have any balanced cables at the time so I'm sure sq was sub-optimal. Saying that, single ended, I prefer the ALO MK3 over the SR71A (by a considerable margin) and Stepdance (smaller). Assuming the 71B is substantially better run balanced and one is willing to invest in balanced cables I can see the value in picking one up used (as the price seems now to be falling). From my short audition it wouldn't be my first choice.
What is balanced/singled ended amp?