I only learned about wasapi last night, and since then I've been doing some trials with winamp and foobar,
 
and I'm not sure if I'm hearing a difference. I'm using my desktop pc with xfi titanium sound card on windows 8 64 bit, but I use o2/odac combo when I'm listening to music.
 
So far I know that wasapi can be used to mute all other windows sound and just play music only, which can be a good thing sometimes I guess. When o2/odac is plugged in through usb, xfi soundcard is 'turned off', and sound is coming from odac only. 
 
 
My question is, does window still mess around with sound before it is sent to the dac? Do I need wasapi to have this 'bit perfect' music sent to my dac without windows doing stuff to it?

Your questions are more related to the Computer Audio forum. You can find more help there.