I think the strap lock I'm using is Jim Dunlop's make, if that helps. I've seen them in most of the music stores I usually visit.
I've never heard of underpowering the speakers and thus blowing them, but have someone else answer you that.
The device you use for splitting the signal can be as simple as a Y-cord, but what you need is an A-B box (or splitter box). They can feed the signal to either of the two outputs or even both,in some cases. I think Dunlop makes those as well.
Merry 100W Christmass!