In your project properties change the audio type from "stereo" to 5.1 This needs to be done BEFORE you place anything on the time line. (If you're using a 5.1 camera then it's probably best to set up 5.1 as your default property so that it always opens as a 5.1 project form the start). Then import your clips to the time line. You will see six tracks in front of you, two stereo tracks for front and rear, and two mono tracks for center and subwoofer. Now you can import ALL tracks as mono if you wish by flicking the "import stereo as mono" switch in your general preferences. You will also see a 5.1 panner for each track. If you plan on using the panner then I would suggest a how-to videos from youtube because there are a few hidden tricks.

You will be able to view, work with, and render your 5.1 without a proper audio card, but of course you will not be able to hear it properly.

Not to disappoint you, but moving sounds around using the panner in Vegas doesn't work the way I would like. I found it very disappointing.
I think it is because the phase relationships are wrong and our ears are not this easily fooled.

Bit like a really bad green screen attempt to the eyes—looks totally fake when you can see the edges.
So too with sound. Mono sounds anyway.

Stereo is perhaps not so bad but you should keep the stereo image centred (ie—in it's original panning form). Panning a stereo image hard left or right gives poor (fake) results.

The only way I have found to produce convincing surround sound (5.1) is to record the source using an Ambisonic mic—then it can be decoded to suit whatever final delivery form you want. However it is not a magic bullet. Close micing an Ambisonic mic (such as a TetraMic) requires close cooperation with the artists and a dash of luck. Or maybe just a good tolerance for imperfection. :)
Here's some artists busking at the foot of Gassy Jacks statue in Gastown in Vancouver, BC.

This is a stereo decode:
http://www.dgvo.net/st/busking-at-gassy-jacks-in-gastown

I recorded this a couple of weeks ago using my TetraMic. When imported into Vegas, encoded with DVDA, burned to dvd with ImgBurn, and finally played back in 5.1 on a home theatre; it sounds really nice.

Like said above, you need a sound output with 6 channels out (most off the shelf PC's due this, odds are your laptop doesn't. You'll need something to send those 6 channels to, like this reciever: here. That's just an example, it has 5.1 inputs (6 RCA's). You'll need cables to go from your computer outputs to that. You'll need speakers on that for your 5.1 setup.

Then just setup Vegas as a 5.1 project. People here suggested using stereo tracks for your front & rears, I preferred using mono's for everything except the music. I haven't done a 5.1 mix since 2007 though, when I had the setup to do it.

Like bdg said, you have to be careful. It can sound "not right" if you don't do it good. I What most films you see in the theater do is they have the music & all voices on the front speakers & the sound FX surround. This is because you can mix the SFX in pretty easily where as the voices aren't. They're recorded from a point in 3D space and the audio they're recording reflects that. To get it in a nice 3d audio setup you'd want to record everyone in mono with mics right in front of them then manually pan those to adjust for the action.

Which is a lot of work. :)

"Not to disappoint you, but moving sounds around using the panner in Vegas doesn't work the way I would like. I found it very disappointing.

Sorry but I find nothing abnormal with the 5.1 panner in Vegas. It works fine.There is however a real art to 5.1 mixing and if not understood and done correctly, then yes it can sound very disappointing. I've been at it for a few years and still have a lot to learn.

" I What most films you see in the theater do is they have the music & all voices on the front speakers & the sound FX surround."

Actually, the dialogue is almost always mono. The music stereo and SFX is all you will hear in the surround.

OP is recording in a theater.
-- Vocals (mono) center front.
-- Music (stereo) L/R front
-- Ambient (house and audience) L/R rear.

5.1 in live venues works, however less is more.

Thank you all for your answers.

My notebook has a hdmi port. Can the multiple audio channels be included in hdmi ?

Anyway, there are cheap usb based audio cards with 7.1 audio, like this one:
http://www.amazon.it/STARTECH-COM-ICUSBAUDIO7D-StarTech-com-Scheda-audio/dp/B002LM0U2S/ref=sr_1_17?ie=UTF8&qid=1384510125&sr=8-17&keywords=usb+soundcard

Then I need an ampli with proper input. I already have the loudspeakers.


I have a stereo front. The stage was divided in 2, action was alternated. So audio in "unbalanced"... I probably should make in mono and put in front. Get the music in the left/right, put the public in back... I may try...

You will not be previewing discrete multichannel audio from the Vegas timeline with a 5.1 or 7.1 sound card. You would need an interface with discrete multichannel I/O, at least six channels worth. Those are entirely different things.

I suggested, from experience, that your best and most accurate preview will come from rendering test files with AC3 5.1, and playing them on your home theater system.
Best.

Certainly true because the discrete 6 channel preview is kind of "dry & naked" preview - it's what is arranged and mixed in your Vegas timeline.
But previewing the rendered AC3 file involves a lot of Dolby metadata which usually alters your output in several ways.