Audacity (
Audacity: Free Audio Editor and Recorder ) is freeware - you might be able to do this using two separate stereo tracks for your music and a third mono one for your voice and mixing them down to a single stereo track (be careful not to set levels too strong and clip the output mix, that sound bad! it could however mean changing the track order or visibility of what is on your "grams" is not as easy as using "proper" radio playout software.
RadioDJ (
RadioDJ – Free Radio Automation Software | RadioDJ – Free Radio Automation Software ) is also free and can do voicetracking but you need a bit of tech knowledge to install it and get/keep it working. (I have experimented with it for running a station that usually plays pre recorded mixes but found that it choked on long recorded files). Those who can get it to work reliably (it seems OK on smaller tracks to be fair) say its better than SAM broadcaster.
Freeplayer (
www.verdonschot.eu ) might also have some of the functionality you want.
Its not 100% clear whether you want to pre-record a show "as live" like how it was previously done with an analogue mixer connected to a tape recorder (hence trying Mixxx, which I always thought was aimed at either "as live" DJ mixing or radio presenting), that is, recording your voice real time over a ]playlist of music - or actual voicetracking which is where all the presenters links are recorded completely separately from the music (often at a different time, from a different place) and the whole "mixed" by automation software...
you might find this link helpful (or can at least have a laugh at the original 1980s era equipment shown there). I'm old enough to remember seeing that kit shown on Tomorrows World :rofl:
Voice-tracking - Wikipedia, the free encyclopedia