Don't think this is the case, since Jan's tone sounds the most Marshally of all three. As far as I know, live he only uses that Mesa Studio preamp during HBTN and FOTD solos. Also, on that picture, I think that's Davey's gear.I think they are probably used mostly by Janick in studio, as Janick is known to having included Mesa Boogie studio preamps in his gear. Recording and mixing three guitarists is not an easy task. Music producers generally recommend recording guitar parts with different guitars and amps to avoid frequency conflicts during the mix stage. So I think Janick probably uses/used Mesa Boogies to avoid this as Adrian and Dave use to play through Marshalls.