Vista - Problems running multple sound devices

I use a program called Virtual DJ for, well, dj'ing. My setup utilizes two
external soundcards/controllers which are run simultaneously for mixing
tracks. On windows xp this works perfectly,but run under vista, the tracks
skip ahead randomly. This is without high cpu usage or i/o activity. This
does not happen if i remove the controllers and use the internal soundcard
(which is not an acceptable solution). Can anyone offer some feedback on how
to stabalize the audio ?