I joined to post about this.
At first I thought the hiby wasn't scanning due to a defect, so I re-formatted the SD card and painstakingly sent music to the hiby via the wireless folder-by-folder. After doing that, I was able to see that a type of file (m4p) wasn't copying over, and they were all old albums I'd purchased from the itunes store in 2008 or before.
It turns out that those files are still DRM protected even after the Apple dropped DRM in 2009.
If that's your problem, you can re-download from the itunes store, rip to a CD or buy software to get rid of the drm. That's 295 files for me, so I'm gonna contact apple to see if there is a more convenient solutions.