All our current guitar amps have a “stealth input” that allows tracks to be inserted. Procure a cable from your music source to a mono quarter inch plug, and insert in FX Return. It will mix 50/50 with the internal preamp signal. After you dial in your guitar sound and level, use the music source’s volume control to balance tracks vs guitar. The tracks will stay clean regardless of guitar overdrive, and the Master will control both.
...unless you have the DirectAmp, in which case, you can do it wirelessly!