john-auvil is correct in that VPX doesn't do multichannel recording, but it certain can do 5.1 mixes and output.
Go to 'Window' (top menues >> 'Mixer' and check that the [5.1 SURROUND] button is active. You should see five red and blue dots above each track column instead of the usual L/R stereo control knobs; You must have 5.1 speakers set with the Windows control panel.
For info on operation search for '5.1 surround editor' under 'Help'.
I've not done much with the system but have found that not all output formats can use surround sound.