Why not ask Bobby? He is very approachable and will tell you as it is.
I auditioned a pair of 8W Welborne Laurels with my TSM-MX's. My room is similar to the size of yours although I have a considerable amount or wall/corner acoustic treatments. I never pulled out the SPL meter but can say that there was sufficient volume/dynamics for late night listening and just barely enough for normal listening levels. I would at least try these 16W amps if your normal listening levels are moderate.
The Art Audio Carissa is a great amp and its power rating is very conservative. It will drive the VSM very well and will suffice for the TSM if you don't listen to extremely dynamic or head-banging music. Bobby, last time I checked, doesn't prefer Art Audio with his gear. I, on the other hand, love Art Audio with my Merlins. Bobby has a strong personal taste towards lush and warm electronics (e.g AA Capitole, Joule) and accessories (e.g Cardas) to mate with his speakers.