Have you looked at the new (2nd) generation mediavault from HP ?
It has twonky also ... Support usb external drive (unlimited size expansion). I have but good thing about it.
If I had the money, I would change my first gen for a second gen without hesitation (even the first gen was good, the 2nd is just ... better).
In theory, there is no difference between theory and practice. In practice, there is ...