I recently purchased a Sansa Clip+ 4gb to specifically use it with the Zune Pass subscription, it works pretty good when you sync it with media player.
I then learned about the Media Transfer Protocol (MTP) and decided to purchase a headunit for my car that supported MTP so that I could listen to it when it is connected by USB cable, I really wanted to avoid the AUX IN since it has a pretty weak battery life when it plays DRM content. I found a unit made by JVC, model Arsenal KDC-ABT22, this was discontinued but I was able to source one. It was a pretty good candidate since it supports WMA DRM content too.
The problem starts that soon after reading the Clip+, it plays the first song perfectly but after that it display that content is not supported. Obviously this unit is capable of playing the WMA DRM files since it plays the first one but after that it somehow just losses the ability to recognize the files or something.