The reason you find different answers is because I don't think they are very rigid in the load requirements. I have run Bassmasters, both the YBA-1 and the mark II, YBA-1A with 4 ohm and 8 ohm loads, for years. You should have no issues whatsoever pushing 4 ohms. I have never tried 2 ohms, and wouldn't recommend it without some confirmation, but it wouldn't surprise me if they could handle that as well. (if it's the higher powered Mark II, it will have "bass master Mark II" printed on the front, and YBA-1A somewhere on the back panel.)