My CS5000 doesn't decode AC3 audio which is a bummer because the PBS channels on G25 are AC3. So I bought a set of Sonic Voom headphones to decode the audio. With these you don't actually use the headphones (although you could) but just connect the little box that comes with them to your receiver and then to the TV. I used the optic cable that came with the 'phones to go from the IRD to the input on the Sonic Voom. The Sonic Voom handles both AC3 and regular audio.
One problem, though: there was a huge drop in volume for non-AC3 audio channels with the Sonic Voom versus connecting the IRD directly to the TV. This is a problem because of the huge difference in volume from other video sources such as my other IRD and my terrestrial digital TV tuner. My solution was to buy two RCA plug Y adapters - they each have two RCA female plugs connected to one male plug. I combined the audio out from the IRD with the audio out from the Sonic Voom and then to the TV. This gives much louder audio for the non-AC3 channels, although I still have to crank it up to listen to PBS.
One problem, though: there was a huge drop in volume for non-AC3 audio channels with the Sonic Voom versus connecting the IRD directly to the TV. This is a problem because of the huge difference in volume from other video sources such as my other IRD and my terrestrial digital TV tuner. My solution was to buy two RCA plug Y adapters - they each have two RCA female plugs connected to one male plug. I combined the audio out from the IRD with the audio out from the Sonic Voom and then to the TV. This gives much louder audio for the non-AC3 channels, although I still have to crank it up to listen to PBS.