I should know, I have one and use it myself with my Maggie 3.6's. Really plenty of power, and the sound is, I think, superb, not much different than, or maybe identical to, the Pass 250.5's.
The thing with the Pass 150.5 is that it's not really 150 wpc @ 8 ohm. It's really like other manufacturer's 250 wpc amps. Explanation: Hi Fi News, the British mag, when they reviewed the Pass 150.5 about 2 years ago or so, found that it clipped at 8 ohms at 270 wpc!! Not 150 wpc. And, at 4 ohms, it clipped at close to 400wpc. I may be off a few wpc in my memory (I have the review someplace here) but not by much.
I use my Maggies in a reasonably sized room and barely have the amp turned up. My friend had the same set up - 150.5 with Maggie 3.6, and felt it was a great match.
If you try the 150.5 and for some reason want more power, you can sell it very quickly on A'gon.