Quoted from sk8ball:
I think he means the songs for police pursuit, stunt car, drift and stampede but they are all under a minute long. The premium/ le the songs for drag race, cruisin, road course, rally race have 8 different licensed songs you can select while on the pro those 4 mode songs are dedicated. Having played both I think the coolest difference is when taking a shortcut on rally race you have to thread the needle to the N2O target without hitting the caution target that pops up.
Actually on the pro, all 6 main modes can be swapped out in addition to drift, silverball stampede, gear shift/drag multiball, burnout multiball, upgrade modes, and Mustang multiball (plus a few others such as the start game, car ready, etc), the same as the premium. The only real difference that I've noticed is that it looks like the premium/LE calls for separate requests for gear shift and drag race multi. On the Pro they both share the same request (stock is Go Boy Go). While we can change all 6 modes, the music is not selectable...each song sticks with it's specific mode.
In all there are 18 songs on the pro that can be swapped out, all of which are long enough to be meaningful and not repetitive. Plus there are a few shorter ones on top of that which do make a difference when changed. 23 total. I changed all but 3 of them (I kept Drag City, Ace of Spades, and the Mustang Multiball song). Once I clarify a couple requests that I'm not 100% on, I plan to document my findings and what I did in the Mustang Music thread that Tullster started.