Amazing but true, mate. Read it and weep.

The nForce APU, combined with NVIDIA's SoundStorm™ solutions, addresses the increasing appetite for full-featured, high-quality, real-time encoded Dolby Digital 3D audio, and greatly surpasses the audio capabilities of other sound cards and sound solutions.

Also found this nice examination of the technology. So again, anyone know of PCI cards that do this?

It does work like Luxo says. I believe it's the same encoder used in the X-Box.

So OK the card can generate an ac3 encoded output for games. That doesn't mean that you can route the six surround busses from Vegas into the encoder and get an ac3 feed on SPDIF.
I'm not saying that you can't, just to be careful as that seems to me to be a different proposition than having the APU feed FXs into an encoder. What rings an alarm bell for me is that it doesn't specifically mention doing that kind of trick, maybe you can but it's all to easy to draw the wrong conclusion in this game.

Also even if it does work there's still a bit of a caveat. Vegas already produces a 'decoded' signal, what you are in effect doing is encoding that and the decoding it again. If I was trying to judge a mix and surround placement there's no guarantee that the nVideo encoder is going to do precisely the same job as the encoder in Vegas when you finally render out as ac3. The Vegas encoder has a lot of knobs and dials to tweak that have a significant effect on the encoder signal.

It also seems to me that it'd be much easier to find an amp that takes the six analogue signals in, there's plenty of units that'll do that including powered monitors at just about every price point.

It also seems to me that it'd be much easier to find an amp that takes the six analogue signals in, there's plenty of units that'll do that including powered monitors at just about every price point.

As I said, I am currently using a setup that takes the six analog mini-plug inputs. The issue is the system makes a faint ringing sound in that mode, and it's quiet with coax input.

According to that third party write-up I linked, the sound from coax is supperior to the analog inputs because the signal is passed to the receiver in digial form, instead of the cheap, analog mini plugs. Enticing. I don't see why the technology couldn't be applied to Vegas busses, but yo'ure right -- one can never be sure.

Anyone using this chip that can offer some input?

I assume the six analogue mini-plug inputs you refer to are in fact RCA sockets. Simplest fix might be to try a different earthing arrangement, either that or you've got a problem with the sound card in the PC. If its one of those AC97 chipsets on the mobo then that's a likely culprit. Insides of PCs and low level audio are never a good mix.

I'm now using a M-Audio Firewire 410 for audio I/O. Difference is staggering. The Mobo mic channel could only manage about 30 dB S/N, now I get better than around 70 or 80 on mic and around 90 on line in. By the time you add some compression the difference becomes even more apparent. Biggest problem now is get somewhere quiet enough to put the mic.

They're 1/8" mini-plugs, not RCA. And I'm runnning them from a Hercules Game Theater XP breakout box. The ringing is not in the source feed, it's inherant to the Logitech Z-680 speaker set. In other words, it rings even when the computer is turned off. It's very faint, but I'm easily irritated. :-)