The obvious differences between the two are the pads. DM5 pro has real drum heads, vs the DM6's rubber pads. I like the feel of the DM5 pro kit's version better (more of a stick bounce/accoustic feel). Out of the box, you can't play along with an MP3 player with the DM5. You can, however, with the DM6. The DM5 is very customizable. I've only owned it for 3-4 days and frankly, it is complicated. The DM6 is much more user friendly.
My two cents. Hope that helps!
Happy New Year