I will try and get over to play with mine and perhaps offer some help. I have a 9600BHS. It sounds like you have used the fader controls. The Mixtrax does have a crossfade control. What model of radio to you have?
Wow, my manual does not mention the fade control so I went digging online. I did find one reference to pressing in the knob and accessing the audio controls. Fade is a basic control so it should not be buried too deep in menus.
According to the manual, the Mixtrax settings are fixed to provide special effects sounds and selected songs. You must have those turned on. Go to the master control MC and select Mixtrax. Start switching the various settings off. What I am reading is that you will have to drill down through the Mixtrax menu to turn various settings off. That should release your fade control if that is what is causing it to be locked.
2015 Ford F-150 3.5 Ecobeast 3.55 Lariat