I'll try ...
Assuming your DAC doesn't contain an earphone jack
It can only be a general outlay though ...
You'd be using Engine#3 since this is the most accurate playback means, I think (well, as intended fort sure).
The means of presenting the data to you DAC (not listed in your "main stream") would be around any interference of the OS and her services (why ? because XX was just created for that and, say, behaves like that or let the rest behave accordingly).
For Vista this would be kind of special anyway, because apart from ASIO there's no other means to do it than how XX does it. This is for a great deal due to the "Exclusive use" of the sound device, that going around all that normally just *will* mangle the data. This is the basis for proper playback.
That this sure is not all, should be proved by Engine#1 and Engine#2, which for Vista 100% sure just do not have this base (hence there the data *is* mangled by Vista), while it still sound wonderfully. But since all is in a context, the context of this is just
here, which not only proves how wrong things can be, but also indicates that this is not stupic commercials only.
But now ...
BTW, I am able to control the volume using the icon that was there before HighEndXX was installed.
Just this would incur for that last mentioned situation, being about the not being able of getting the sound device exclusively, that by itself causing the SRC (sample rate converter) of Vista jumping in, no matter nothing is there to be resampled.
As far as I have found, this is related to what you mention in your signature :
Microsoft High Definition Audio Deivce
which by now to me looks like some kind of hoax since the last thing it seems to be is "high definition" (well, according to MS all which is resampled is for the better of "you" the Vista user).
Rupe, I was taking a presumption on you using Engine#3 (of which I have this example of "HD Audio" on my desk which behaves the same as you just told) which doesn't seem to work ever with this "class driver" device. If you were using #1 or #2, then try #3 first before I'm screeming (okay, I already did
).
Does this help you in some way ?