July's Modern Railways states:
-12-car sets are two six-car sets back to back, with a power bogie each end of the 6-car to make four power bogies in total.
- Confirmed two power bogies on a 3- or 4-car set, one each end.
- One power pack in 3- or 4-car sets.
I think we can therefore conclude that the articulated bogies are unpowered. My guess is that the power packs are all the same, approximating to the rating of the traction motors in the two bogies. These are also of course likely to be the bogies with the lowest axle loads, and no rail conditioning for the one at the front. But you'd expect with their experience of building for Alpine railways Stadler would know about adhesion.
Leading bogie being motored is not smart idea if you want to minimise repair bills and time when you hit things on the line. (Rural areas with lots of level (inc farm) crossings...).
The axle loading and unsprung mass would be very high if they motored the articulated bogies leading to massive track access charges.
The main design driver for Stadler were cost, cost and cost