Stan,
Your question of will the XA-100.5 do the job needs to be clarified. How big is your room? What type of music do you listen to? How loud do you like to listen? All will impact what will meet your needs and satisfy you.
While I'm schooled and licensed as an engineer, I gave up explaining things scientifically quite some time ago (not that there's anything wrong with that). I prefer to explain how equipment sounds. If someone asks - circuit design, component selection, circuit board topology, power supplies & filtering, component configuration, dampening factor, slew rates etc. can be discussed. I believe it's simpler and easier to describe what works well and how a component sounds.
George is spot on referencing an amplifier needing to be able to supply power into a low impedance load. This is especially critical for amplifiers of (relatively) lower power output. However if an amplifier has a (relatively) higher power output, say 100 watts instead of 30, it can still provide adequate power (current) for low impedance loads even though it doesn't quite double it's output current.
While the Pass 30.5 suffered reproducing dynamics, it never embarrassed itself. It simply wasn't as convincing in a comparison to a live performance.
If listening to the 100.5 and 160.5 with Sashas isn't possible, I'm confident to say the 100.5's, even the most demanding music (anything with big dynamics) with a moderate sized room and lifelike volume, won't disappoint. The 160.5's will always sound better but upgrading is another story. We got the 200.5's on a deal I couldn't pass by - we intended to purchase the 100.5's.
Hope this helps, TJF.
