One of your threads is in the M6 forum, this is in the iMX6 area, which device do you have?
Can you temporarily share a folder on your PC, and drop a few tracks in there.
Mirror the setup/playback method that you're using with your NAS, and we'll see whether the problem remains.
Also, I'm assuming the music skips in XBMC? Did you try Ahmed's advice in the original music skipping thread, re. clearing the data (then re-running the wizard)?
Can you try using the ES File Explorer application, go right one screen to the network window, add your NAS as a network location, and play the MP3s outside of XBMC this way?
Hopefully finding where the error changes will help us to fix the original issue.