Yes, I am away at AmiWest, I have not been reading or posting for a few days.
Having said that, this is a brief partial response, there will be more info later once I am back at home on my machine.
re:24 bit vs 32 bit.. there is no difference in these AT ALL.
What AHI calls 32 bit is "A 32 bit package, carrying 24 bits of audio sample"
What the HDAudio/Envy24 devices consume (both) is "24 bit samples carried in 32 bit packages"
In other words, they each have a different description for the exact same thing. 24 bits of sample in a 32 bit word.
The two devices are probably quite similar, but since I don';t have an Envy24 here, I can only compare one of the two:
Maximum playback rate will ahve a lot to do with it.. HDAudio goes up to 192 Khz, and I CAN definitely hear less noise at the higher rates. I don't know what the envy offers.
The Envy (or at least SOME of them) offer balanced outputs, which should provide a lower noise floor compared to the unbalanced outputs of HDAudio. Whether or not this is significant depends on your situation and what external equipment you are using.
The option for using optical outputs is an equalizer, offering two advantages, you can now isolate the grounds of your computer from the ground of your sound system, and you move the actual Digital to Analog conversion to your receiver, instead of the one on the sound card.. This effectively nulls the "balanced" advantage, and adds ground isolation as well.. BUT it limits your max sampling rate to whatever the upper limit of your S/PDIF receiver, often a bit lower than the 192Khz of the HDAudio chip.
Yes, there are many details missing, but this is all I can offer from the floor at AmiWest. Feel free to ask for more details, but don;'t expect much of a response before Wednesday.
LyleHaze, reporting from the main floor of the biggest Amiga Party in the continental United States.