Change to pass-through behaviour for DTS-HD

The problem is not that there isn’t a work-around, the problem is that the way it works now is highly counter-intuitive. I expected it to already work the way I’m describing, and was surprised that it doesn’t. If you check out this recent thread you’ll see that two other people there make precisely the same assumption. As it stands, people are going to get sub-optimal audio without necessarily realising that they are.