I've used the PL 6 monos with my VSMs for about 3 years now, with great results. The PLs allow tube rolling and the character of the amps (at least mine) changes pretty significantly with the choice of output tube. My PL amps are a pleasure and I think most people will be happy with them, but, with highly transparent speakers like Merlins, the question of output tube choice might be as relevant as the choice of amp. At least, that's been my experience with the PL/Merlin combo.
Over the course of the first year or so that I owned the amps, I systematically ran thru a bunch of different output tube types, because I was essentially just running an experiment to see which I would choose for the long run. I ultimately settled on KT 66s as the best overall balance of upper bass definition, bottom end weight and midrange appeal. Depending on your personal priorities, however, your conclusion might well differ.
Further, since the TSM doesn't have the low end extension of the VSM, the issue of bottom end weight probably becomes less important to your evaluation. You'll have to decide for yourself if the relatively subtle difference in reproduction of a kick drum is important to you. I don't think (to be honest, I don't really know the TSM, so I'm guessing and could be wrong) that you'll hear the more evident delta below 45ish hz. (the lowest registers of electric bass, for instance) on the TSM. That might tilt the TSM equation toward Bobby's preffered EL34s.
In any event, with the PLs, you'll have the opportunity to decide for yourself. I think they're very good amps, very versatile, very good value, and - with the right output tube - a very good match for Merlin.
Good Luck,
Marty
