Thanks! I've had Belles Aria monoblocks, AVA M225 monoblocks, and the AGD Tempo all plugged into the Puritan at different times, and in all combinations there was the same improvement over without the PSM156. Nothing more powerful. I really don't believe the Puritan is current-limiting. There are one or two long threads about it over on AudioCircle--you might find users there with the kind of amp you're curious about.
The M225's are very good. They are little powerhouses. Given their topology, I wouldn't necessarily choose them for speakers with very low impedances, but then the Harbeths are above average in that regard. They get out of the way. The comments on them over on AudioCircle tend to wax very lyrical; I'm not sure I would go that far, but they let the rest of the components shine and don't hold them back in any way. And--a bonus--you don't need an engine hoist to move them around, the way you do with many 225W amps!
