It really depends what you mean by wanting to play “different audios at the same time on different speakers”.
You can use the Channel Mix effect to force only certain channels to output audio, essentially muting one side of speakers, or you can use the ChannelControl::setMixMatrix() if you are using the Core API.
If you are referring to outputting to multiple audio devices then you will need to run multiple FMOD systems. This is basically just running every single FMOD command twice to two separate instances of the FMOD system, but it will double the resources required to do so.