Yeah, its possible, i did exactly this when i first started up again – but with a Numark DXM mixer
At the time i already had a Citronix external soundcard for ripping vinyl to the lappy, http://www.chemical-records.co.uk/sc/servlet/Info?ref=gbase&Track=SK128515
So i bought another of these and configured each VDJ channel to the mixers A & B channels on the line in’s while still having the vinyl turntables on the phono in’s, a flick of the switch and i could use vinyl or the laptop as a source
I still keep this pair of citronix cards as a back up if the midi goes west, i can just plug these in to a house mixer using VDJ as decks and the mixer to cue and bring in tracks
you CANT do this with traktor Scratch pro 1, you need the NI audio cards or DJio or equivalent – i dunno about the latest version of Traktor though, i havent tried