I checked around the net a bit on this camera.... there isn't much info on the audio. It seems to feature "recording in PCM" which may differ from the typical DV cam. They may be referring to the additional channels 3/4.
I would first try Scenalyzer to capture, (as Jet suggested), and see if that can capture audio and video together.
Capturing audio separately could be a big pain. You could *try* to start Vegas audio recording while capturing with Vegas-Capture, but I wouldn't get my hopes up of a clean, sync capture... video or audio.
I don't think it would be practical to try capturing analog audio at the same time as capturing the video through firewire. I'd go for a two-pass method, capture the video, rewind the tape, then record the audio. You'll still have to deal with the same sync problems either way, but you risk more dropped frames and garbled audio if you try to do both at the same time.