No, its matx, at least the dt and mt models are i think. However, they do not use standard fan pinouts and the front panel is propriety, so with a new case you'll have to jury rig the front panel it comes with, or just find the pinouts and go from there. I have a 790 dt, I'll come back later after seeing if it fits in an atx case.
Just checked, It fits, but the front panel is, once again, totally different.