@reiserFS, yes it works with Mavericks GM and the latest iTunes 11.1.1. Only issue I had during the beta period was with a pre-release version of iTunes from one of the earlier preview releases of 10.9.

First, I suggest you contact Jason at Schiit about this. They don't provide a Windows USB driver for Modi, it's using the native USB audio driver, but they may have some suggestions to help resolve this. And good to let them know if there is an issue with Z87-chipset motherboards.   Second...

I know a couple of years back people were having trouble ordering these even though they were listed on the UE website. Just to let people know, I ordered a set last week and it shipped a couple of days later. So whatever problems UE had keeping these in stock back then seem to have been...