If you are talking about running AFSK via FM, you usually cannot take the audio from the speaker or send it to the mike input when running 9600 baud (you can for 1200 baud). You need to get the receive audio directly from the discriminator output and send transmit audio directly to the modulator, avoiding the pre-emphesis and de-emphesis circuits in the transceiver. Some transceivers have a data connector which has inputs and outputs intended to be used for 9600 baud. The equipment manual should give you that information.
790 has no 9600 band FM input support. I was assuming he was using AFSK here.