Sony Vegas and importing multichannel audio

Hello.

I have Sony Vegas Studio HD Platinum 11 and I've had a crew shooting a film.

In cases where there are three or more microphones, if I drop the file into Vegas, I am told The Number of Channels is Not Supported.

I've tried making the default audio under preferences 5.1, with multiple audio tracks, but it makes no difference.

Is there a way to natively drop the file in for editing?

If not, is there a free utility to split the multichannel file into independent files as a wav or aiff and edit that way?

Thanks in advance.