copying itunes library to hard drive issue
I'm trying to copy my entire itunes library on my office iMac (OS 10.6.8 / 3.06 GHz Intel Core 2 Duo / 4 GB ram / iTunes 11.4) to an external hard drive that I can then plug into my Mac Mini (OS 10.9 Mavericks / 2.5 GHz Core 2 Duo / 4 GB ram / iTunes 12) at home that I'm using as a dedicated music server. The Mini is configured to use the external hd for the itunes library.
I copied the iTunes folder to the hard drive (after consolidating files) and everything appeared to transfer over. I use a headless Mini and control iTunes via the remote app on my iPhone. The issue is that a third or more of my library seems to be missing, and album art that I've updated in iTunes on my iMac is not appearing in the transferred library. Some music won't play because "the original file is missing."
Is this happening because the iTunes versions are different on each machine? I can't upgrade iTunes on my iMac until I upgrade my OS which I'm not doing yet out of fear that older peripherals will no longer work. Any idea what's going on? Thank you!
iMac (27-inch Late 2009), Mac OS X (10.6.8), Safari 5.1.10