A:
Wendy,
The Rocketfish works well for me for small surround speakers. The information provided with the unit doesn't indicate the amplifier specs, but it is not very large in size and is probably designed to drive very small speakers typical for all in the box surround systems.
I would question whether the unit has sufficient power to drive larger speakers, and when you say "12 inch" speakers, I can only assume that you are referring to cone size. If the speakers are truly that large, I wouldn't expect the Rocketfish to drive them very well. If you are referring to the speaker cabinet size in some way, then maybe you have a better chance of it working, but even then you might try to get some info from the manufacturer.