I finally got it to sync completely. The process I used is as follows, and may be repeatable. NOTE, I am using a 2010 iMac running the latest version of Mavericks, and an iPhone 6 Plus 128GB. Here is the workaround process I came up with that finally worked. Hope it helps someone:
Step 1: I put the iPhone into Recovery Mode, connected it to iTunes, and restored it to do a clean install of the software on the phone.
Step 2: Using a lightning cable I synced everything EXCEPT for music. (Apps, TV Shows. Movies, Tones, etc) For me this took a couple hours and completed without any issues.
Step 3: Once this completed, I checked "Sync entire music library", applied, and left it running overnight. It showed 9200 items being copied, and showed a blue progress bar underneath, and flashes the individual names of the files in the status bar as they are being copied. Once it gets to the end of the 9200 items, and the blue bar gets all the way to 100% it gets stuck on "Waiting for items to copy", and never completes the sync, no matter how long I leave it running. Checking the Storage stats on my iPhone under General Settings/Usage reveals that not much is going on. The stats change by .1GB (100MB) every so often, but not much more than that over 12 hours. DO NOT INTERRUPT A SYNC WHILE files are transferring and the blue progress bar is moving! Doing so in my case resulted in all subsequent syncs getting stuck immediately and indefinitely on "Waiting for items to copy", which seems to only be able to be remedied by Restoring again.
Step 4: Once the blue progress bar has reached 100% and Sync gets stuck on "Waiting for items to copy", cancel the Sync by pressing the X in the status bar, and reboot iTunes with iPhone still connected via lightning cable.
Step 5: Turn on "Sync over Wifi" and press APPLY. Disconnect lightning cable, and reboot iTunes again. (Cancel any Sync that is in progress)
Step 6: Make sure that the computer is on the same WIFI network as the iPhone (preferably a dual band wifi network with both devices in close proximity to the router) Having the computer connected via ethernet, and the iPhone connected via WIFI will not work, even if they are using the same router. They both need to be connected via WIFI, and I took the extra step of disabling the ethernet connection. It is a good idea to plug your iPhone into a charger at this point (not the computer) as this process seems to be rather power intensive. This does not seem to interfere with the sync over WIFI.
Step 7: After you see that the iPhone is connected to iTunes via WIFI (it should appear on iTunes like it normally does when you connect it using the lightning cable. If it doesn't check that both devices are on the same WIFI network, and that "Sync over WIFI" is checked), then press Sync, as it does not seem to sync automatically via WIFI, even when "Sync when connected" is checked. In my case, iTunes suddenly found another 2000 or so music files that did not sync automatically during the previous sync over the lightning cable. These once again show progress with a blue status bar, and the names of the files being transferred flash in the status bar as they are copied. This took a few hours.
Step 8: Once the transfer of all the files completes, the message "Waiting for items to copy" DID appear again for a few minutes, but it didn't freeze there indefinitely this time. DONE! In my case I did get a warning that some of the items failed to copy (11 items) but this is the same message that I have always gotten in the past. Apparently these 11 items in my iTunes library are incompatible with my iPhone. I keep hoping someday that a future update of iTunes will be smart enough to convert these 11 files on the fly to a compatible format, as the rest of my music is down-sampled to 128K. (I have my iTunes set to convert all music to 128K when transferring to my iPhone to save space. This option is available on the summary screen when you sync the iPhone in iTunes.
NOTE: Regardless of whether your Sync is getting stuck on apps, music, or something else, the key seems to be to transfer as much as you can using the lightning cable until it gets stuck, and then switching to WIFI to transfer the rest. Good luck!