ALL mtx 2 channel amps (and most other brands) are only bridgable into a 4ohm load according to the manufacturer. anything below 4ohms bridged you are running a risk of damaging the amp!
because when bridged @4 ohms the amp sees a 2 ohm load because you are series wiring 2 channels into 1 so same thing would be said for bridging into 3..the amp would see half the load due to the wiring thats why i would ask mtx outright....they have great tech support use it