The program that we've had the most success with is "CoolEdit".  It used to be produced by Syntrillium, but was recently bought by Adobe (
http://www.adobe.com/special/products/audition/syntrillium.html).  I am not sure about the latest version, but CoolEdit 96 and CoolEdit 2000 have great batch-processing features to automate the editing of multiple files.  CoolEdit also supports Dialogic VOX format natively. 
Another one that's gaining ground is Audacity (
http://audacity.sourceforge.net/download/).  I am not sure about its features, but the price is right. 
I believe the VoicePlayer's converter and the Designer's converter are the same, but for safety, use the Designer.  That is the one I always use.