you need an external audio input.
basically what this is, is a shielded audio cable that goes from your audio chip to an external input jack, such as an RCA female, or a 1/4" female jack.
the center conductor of the cable goes to whatever pin is the audio input pin, and the shield goes to PC board ground.
the other end of the cable goes to the jack.
yes, you will have to put some series, and/or parallel resistance inline at the jack to get the levels right.
also, you will need to isolate the jack's body from the metal chassis if you mount the jack to the metal of the radio. otherwise you will short the PC board ground and the chassis ground together.
tell me what kind of radio you want to do this to, and i'll see if i can help.
once this is done, you just make up a simple switch connected to a mic plug that will plug into your CB, so that when you switch the switch, you are keying and unkeying the radio.
mine is a big toggle switch because it looks cool and stays keyed up without my hand being on the button.
now, plug in a mixer into the external audio input you made, and you can run as many effects as the mixer has channels.
plug your bass into a D/I box (if needed), then into the mixer, and you can play your bass over the air!
the cool thing about this is that the sound will still come through your CB speaker so you know what it sounds like over the air.
i have my 2000GTL set up to do this, and i can use whatever reverb/phaser/ whatever else my zooom box will create, and i can mix that sound with my voice, coming through whatever mic i want to use. (i like a shure SM-57)
then, if someone starts whining (truck drivers LOL), i grab my guitar and start playing some blues riffs along with them. LOL
"my radio just wont get out over these damn base stations!" (nah nah nah nah nah!)
"and i dont know where im supposed to go because i didnt look at a map" (nah nah nah nah nah!)
oh its sooooo much fun!!!
good luck,
LC