The emulation of a human voice can be done by setting several BP filters on the sound.
In the virus, you can use two BP filters with reversed polarity.
The cutoff & rez settings will give you the vowel you want.
The ADSR on the other hand will only control the way the sound is played => short, long, aggressive, smooth ...
Check out Cosmosis interviews, in one of them he explains how he creates his formant-like sounds on the Virus :
http://www.cosmosis.co.uk/cms/