TerraSin
Running Twin Duo USB on Win 10 just fine. Not sure why they've not announced official support yet.
I had a very productive chat with their support folks last week on this very topic. I had been frustrated a while back by the lack of official support for Windows 8 (which admittedly I had not checked before upgrading.) It worked, but there was a minor glitch with one of the installers - which was resolved in the next release, even though Windows 8 was not yet officially supported.
This may even be on their site somewhere, but the short version is this - they only officially support those operating system versions - and platform versions - that they are actively testing. And they are actively testing the operating environments and platforms used by the majority of their customers. As more customers use Windows 10 it will get suported.
They just can't test everything, it's not a huge company. He did say that they are testing Windows 10 now, and anticipate announcing official support for it in the near future (no dates were provided, imagine my surprise.)
In the meantime (and Billy Buck can confirm) they do take advantage of their diverse user population - if you wonder about using a specific device in a specific environment you can ask on their forums, or sometimes even their support team. Not to pick on Billy, but I believe his system is almost always on the leading edge, meaning he is using their hardware in environments that are not yet officially supported. And they work.
UA can be a tad frustrating at times, although they are getting better. And their hardware and software is definitely on the expensive side. But dang, it sounds great!
For the record, I am currently using an Apollo Twin USB and a UAD/2-Quad PCIe card on a homebrew PC running Windows 8 and 10 (still sorting out 10). UA has caused me no problems! Come to think of it, I've really not run into any problems with any of my essential music production tools. I'm probably about ready to throw the switch once and for all...