Hello,
Can the Sixtrack Software function as an ActiveX server? Communication from LabVIEW to other software programs is MUCH easier with ActiveX than with DDE...that's why there are so many more resources out there for LabVIEW and ActiveX than for LabVIEW and DDE. Nevertheless, there are some examples on the NI website for DDE communication with LabVIEW, if you haven't seen them already.
Also, I did a cursory web search for "sixtrack labview" (without the quotes) and found about five hits, some of which seemed like they might be able to help...at least you could get contact information for people that have worked with Sixtrack hardware and LabVIEW before.
I hope one of these suggestions helps you with your application. Good luck, and have a good day.
Sincerely,
Darren Nattinger
Applications Engineer
National Instruments