G5 analog audio out 5.1 capable?

I dont' think "5.1 headphones" exist since by default there are only two sound sources, left and right.

To answer your question - no. 5/6/7.1 sources can't be output through a 1/8 inch audio jack. USB/Firewire/Coax/Optical connectors can do this. You'll need to use your optical connector for true 5.1 sound.

For those without a G5, use the USB out and get this, which will get output 5/6/7.1 surround from a laptop etc:

http://www.m-audio.com/index.php?do=products.focus&ID=ce4f3b6d13494004f69f07cb11070055

 

Well, technically 5.1 is possible because of the number of channels used, but think about how it's encoded. Signals designed to come out of the "front" will be millimeters away from the same sounds designed to come out of the "surround" channel. Your ears can't hear the difference in sound depth. It's a glorified stereo signal, but if you want to try it out, we'd love to hear the results.

 

That's a fake 5.1 you are talking about. The only way to achieve true 5.1 is with 5 speakers/sub and 5 independent out sources.
By modulating channels and frequencies you can only change sound so it appears that it would sound somewhat like lets say it would be coming from behind. Any 2.1 system can do that but if the speaker isn;t located behind you but makes a sound like it is... well you get mediocre results. Although for headphones, of this quality, I'm quite certain it would sound very well.

 

We localise sound direction by analysing the time differences between sound reaching one ear then the other, as well as recognising the tonal differences between direct sound and sound that's been reflected or absorbed or refracted and a number of other time and frequency based artifacts.

Consequently no earphone system can ever create the same spacial characteristics as separate speakers. I doubt those headphones will do anything other than offer a phase-matrixed stereo feed.

The stereo jack/cable in analog form can't carry the 6 discrete feeds anyway, so they could stick 50 speakers in and they'd still all play the same thing.

If true 3D sound was possible from stereo speakers don't you think the big manufacturers would be all over it?

Still, the USB digi out looks very cute.