You can run whatever brand you want. If your battery is large enough (standard G24) you should have no problem supporting both units at the same time.
The trick, like mentioned above, is to make sure you don't overlap the two sonar sources - this can be done by making sure you use different frequencies (83Khz in the front, 200Khz in the back), or by allowing enough distance between them provided you're fishing relatively shallow water.
So - an 83Khz sonar cone has an angle of roughly 60deg, which if using a rough guesstimation on size, is about a 1:1 ratio - thus if you're fishing in 8' deep water, your cone area beneath you will be about 8' around in a circle. SO! If you've got a transducer in the front of a 14' boat at the same 83KHz signal, it will also have a cone about 8' around at the front of the boat, leaving you with an overlap in the coverage areas - this is where you'll see the interference as the sonar's not sure where the extra signal is coming from. Changing to the 200KHz signal will change both the cone angle (about 20deg) narrowing the coverage area, as well as changing the return frequency to the transducer so this will cut down on cross talk.
Hope this helps!