depends what kit you are using/radio. i know on the hog tunes kits i have installed in the fairings of ultra's it mounts right above the radio and works great with no problems. on the fairing i made for my dyna i made a bracket/cage to mount the amp below the head unit on mine, no issues at all on the stereo or radio functions
been running 2 amps atop the radio on my ultra for 2 years without a problem. just changed the amps to the J&M 4 channel about 2 months ago.. no problems.. the J&M kit allows you to relocate the XM module and CB module below the radio.