I haven't heard of an "upgraded" Post-Show Discussion for subscribers. I'm a part of their HIPTIX Gold program and from my experience, which performers come out after the show during these events depends entirely on the individual. I attended the last Celebrity Series for The Real Thing and all the actors came out to discuss the show and take questions. Since their 2012-2013 season I've attended a Post-Show discussion for every one of Roundabout's shows and the turnout is actually pretty good.
"Mostly, I loved the size of these people's emotions. Nobody has emotions this size anymore. Outsized emotions. Operatic emotions. Kushemski and Vanda are like Tristan and Isolde, they're Paolo and Francesca. Nobody's in total thrall like this anymore. Nobody's overcome by passion like this, or goes through this kind of rage." Thomas, Venus in Fur