Just an FYI, the Vidars are not designed to drive lower impedances than the Aegirs. They may do better at it but both amps are designed with the same loads in mind.
Duly noted.
For what it's worth, though, and not to start an argument but simply as mere added information:
I've had them for a bit over a week, and they haven't shown any sign of struggle. Their frequency response seems stable at all (relevant) volume levels, and the amps themselves remain very cool to the touch. They barely get warm at all, especially nowhere near as hot as the Aegirs. (Yes, I know, apples and oranges.)
Schiit also specifically mentions in Vidar's FAQ section that magneplanars (which tend to be at around 4 ohm, dipping down to ~3) are no problem. Granted, that might be assuming a single Vidar in stereo, but it's not specifically stated that they wouldn't be able to do so as mono blocks, either.
So, worst (albeit somewhat likely) case: I'll have to use a single Vidar in stereo once I pull the trigger on the Magnepans.
Until then, I think they'll do fine with the Q950s in mono.
And if not, I'm sure I'll be able to find a more suitable alternative, although I'd hate to have to go outside Schiit.