I haven't heard of any 990 mods. In fact, the only Outlaw product I've ever heard of mods for (aside from barend's transformer surgery to allow a 7700 to run natively on a 220V grid) is for the old Model 200 - there was somebody doing a fairly pricey mod that included adding a balanced input (among other things). Now that the 2200 is around and already comes, I don't know if there's much happening there either.