define: sufficient for voice
On a ventrilo server running GSM (the standard if you don't use shitty speex wee sample with 16bit 44.1Khz

digital signal will have to be converted to analog eventually but usually through individual drivers in order to produce something with true surround sound (I.E. Razer Tiamat)

and as for who would do that
I did
I payed 250 USD for a sound card that can output and input optical signal at 24 bit 192Khz because I don't want any quality degradation... in order to pay additional money to have them fudge up this perfect signal is unacceptable