How much power for Merlin VSM speakers?

I bought a pair of Merlin VSM-MMs and am driving them with a Cary SS amp. While it sounds pretty good I am thinking of switching to a tube amp. I am familiar with the usual OTL suspects most people use like the Berning and Joule. I was wondering if there is anyone out there driving these speaker with a less powerful SET amp. How powerful does the amp have to be in order to not clip? Is the speaker efficient enough and its impedence curve benign enough for low powered amps? Is 30 watts enough? Am I asking the right questions?