I Second what @Dave Matney has said - I get quite a few showreels sent to me and I can tell you now that and the ones that get the most attention are those that are easily accessible i.e. streaming via the net. DVD's or CD's of music through the post are a pain because our whole recruitment system is online so you can't add links to their work, bookmark things I like for future reference or send the examples off to other team members to evaluate without added complication. As for the playback format - here is an example from where I work - a potential employee's/freelancers showreel would start off with me who can play back 5.1, but then go to our Art Director and Creative Director who both have 2.1 systems with far too much bass, but they may well listen back through headphones anyway (and one has a PC and the other a mac so WMV isn't the best choice). Then go the the Art Manager who will be listening on headphones and can't play back 24 bit files, and won't have any codecs installed. I'd guess this would be similar in most games companies. So basically my advice is 5.1 is great! but make sure it translates well into stereo and more importantly than anything is a well balanced mix. If Vimeo does 5.1 :) that sounds like a winner.

Assume that your demo will be viewed / listened to on a stereo device, unless they've actually ASKED for your demo. Vimeo does not support 5.1, though, so people that want it can hear it there. (see below)

Also assume that no one is going to ASK for your demo (someone will, don't worry, but assume that no one will). They're going to go to your website and maybe watch the first 30 seconds of it, and make their decision from there. They're not going to download something to burn it to a DVD and play it in their home theater -- if it's not streaming, they're not going to give you even 30 seconds.

So, in my opinion, if you plan on developing a 5.1 demo, make it your only online demo, and make it available somewhere where surround streaming is supported. Make it also compatible with stereo systems. Don't give someone the option of "Surround Sound Demo available on request," just make that the only option.

UPDATE: Official word from Vimeo is that they don't currently support surround sound, and they don't comment on upcoming features. BUT, Flash 11 just dropped, and that does support up to 7.1. (Also, Microsoft Silverlight supports surround) I would expect Vimeo to support surround sound in the near, if not very near, future.

EDIT: G'day, work in DAWs, AM broadcast and digital broadcast. I have no experience in preparing audio for surround systems, but seeing as no one else has replied, I'll get the figurative ball rolling.

So... the question is what format the audio is mastered to? Well, I don't know why you'd be using a lossy format unless it's the only format the playback system can read. (which is pretty surprising) In which case, if it's the only format it can read, then shit, I guess that's your answer.

If you target systems can only read one codec (really? in 2011?) Why not make different demos for different systems?

(Am i missing something and being really stupid here?)

When I send DVD copies of my reel out on the label I put a 5.1 surround logo on there so that if a perspective client has the ability to listen in surround they know to. The down mix is always supplied so the stereo will play if 5.1 decoders are not recognized.

Spencer