Welcome! Well, welcome to the world of posting.
If the right people see this, you should get some real good info. There's a number of knowledgeable people here on this topic.
After reading your description (especially the mention of iTunes and 2 TB), an Apple Time Capsule came to mind. I don't know if that's any different than a NAS, but I know that people use them as music servers. They come in 2 and 3 TB versions, and I'm pretty sure that you can connect an external hard drive to them for even more storage.
Another product that popped into my head was a Popcorn Hour. That's a media server, though, so maybe not what you want. A member here,
Warpdrv, posted
two of them for sale last month. He might be able to give you some good info on them, and I know that others here have used them.