No I think I was the one confused not you.
The PP150 became the PP120 SST because we wanted to keep the size of the chassis the same as the old PP120. The reason is that a lot of people mount the PPacks on the rear of the PMC speakers and keeping the physical demensions the same was important.
Therefore the heatsink could not be made large enough to output 150 watts so we stayed with a 120 watt rating. The PP120SST although rated at 120 is really putting out about 145 - 150.