I ran into the exact same problem when I switched from Verizon to Sprint. I found that root or no root, button control app or no, the phone still worked the same. Rooting may open more possibilities, but it's not a solution on its own.
My solution was to buy a stereo bluetooth headset with media controls. Two others may be GO Locker and Widgetlocker. GO Locker allows you to launch a program from the lock screen using a certain gesture, and is free, while (from what I've read) WidgetLocker allows you to put widgets on the lockscreen (such as the music control widget), but costs a little bit.
There may be other solutions as well, but these are the ones I've come across and am most familiar with.