The only reason (that I can think of) for wanting DD5.1 on the IO would be for DVD playback as VCD's are not surround sound (though I suppose they could be) and Surroud Audio CD's use the DTS standard (though these are hard to come by).
You can get a speaker set from Creative Labs (hifi.com) for a little over 100 bucks that comes with the full 5.1 speaker setup and a dolby digital decoder built into the center channel (or the sub, I'm not sure....)
If you were to put a DVD player on your IO's IDE chain (like others have done with CDROM drives), you could use it and a software decoder to play dvd's on your io, and output the sound via the players digital output (most have these, it'll be either optical or coaxial) to the speaker/decoder setup. Note that as of yet, a hidden pci slot has not been discovered on the io's motherboard, thus the software decoder. I suppose you could turn off the video decoding and just listen to the sound (for concert dvd's and the like). Otherwise, DVD playback would be WAY too taxing for the Winchip 2 or Rise 266. If you were to, say, get a RAM upgrade and a K62-333 upgrade, DVD playback would be feasible, but still nowhere near optimum. Software DVD decoding is very taxing.
As far as your speaker setup goes, I know of no way to get surround sound from placing speakers in front of you and behind you. In fact, that would be a REALLY bad way to create any kind of surround effect (except for, I suppose, an airplane passing over your head from front to back). You would lose any lateral stereo imaging, which is far more important to conventional surround sound than front/back type effects. In an optimum dolby digital setup, you don't even have any speakers behind you, the 2 surrounds are actually placed to the sides. Though DD 6.1 EX and DTS ES change this by adding a virtual rear center channel to the mix.
And on top of that, the IO screen would be horrible for movie playback.
So in conclusion :), I guess you COULD get DD 5.1 from your I-Opener, but why you would want it beats the hell out of me. Maybe get a DVD player with built-in TV-out, the DD 5.1 speaker set, and use the IO (with touchscreen) as a super DVD navigation system (hey, that actually sounds cool!). Unfortunately that would require writing your own DVD playback software, which according to the MPAA, RIAA, and others, is highly illegal, and poses a threat to the foundation upon which this great nation was founded.
Hope that cleared things up a bit.