Bad news, output voltage is weak. I measured 0.6Vp-p. Not good. I am disappointed by this.
Iceman-
Still the same as far as line in goes. It was a little tricky to get it to even work, but you are correct. Muting line-in on windows mixer does nothing. However, if you are using ASIO I beleive you would have to use the Audiotrak mixer control panel anyways since ASIO bypasses the windows mixer.
I don't have anything going into line in so it does not botther me, but I will add it to the cons list. You could always use an relay or switch to cut the line signal off.