Vegas 6 can create a AAF file ( a EDL on steroids- if i remember correctly Avid is the creator of AAF ) … look at the specs of avid express pro to see if it can read AAF files ??
keep your vegas TL simple !!! it is not going to export 14 layers of compositing and avid takes in in correctly etc .. simple video tracks with sync audio ( do not split the channels) , simple transitions – i do straight cuts … make sure all media is orginal ( not a video where you have rendered sections in it ) unless the avid has access to those files …