<p>My computer has two external audiocards and one in the motherboard with windows vista. In Vista it sees two entities for the same soundcard, a digital- and a analog output. </p>

<p>When i try to play an videofile with digital audio, say an dvd, it chooses <em>'Default DirectSound'</em> whereas i want it to use '<em>Digital Output Auzentech</em>'. So i thought easy enough, i just change the merit for 'Digital Output Auzentech' to a value higher than the others, so it would be picked, when a application tries to build an play-graph. </p>

<p>The problem i have is that all audio entities has the same id, so by changing 'Digital Output Auzentech', the 'Default Direct Sound' gets the same merit. I believe to have searched google-dry for information about merit, directshow and audiorenders, but still haven't found an answer.</p>

<p>Maybe some of the bright minds, who hang out here could help me </p>

<p>(tools i have used is GSpot and GraphEdit on a Vista Ultimate 32bit)</p>

Why would you want to tinker with "merit" of directshow filters? Won't that be a bit overkill. Digital audio or not in your video file, you can use any output device here. So you can even stick your 'Digital Output Auzentech' for all the audio on your system, not just for dvd.
If you just want to select 'Digital Output Auzentech' for a particular apps, then I believe most decent apps let you do that. If you want to do and overrides all your apps (not the apps setting but it's windows' default setting), then head to "Sound and Audio Devices" under control panel (this is for xp, vista had something similiar, but I can't recall it's name), under audio tabs, change your Sound Playback Default device to 'Digital Output Auzentech', that's it. Then all your audio will be output from it.
Personally I use Media Player Classic, if I have AC3 or ACC track on the movie, and prefer to enjoy full digital output, I can easily switch from the Sound Filter settings.