Ofc you can carry the audio to the HT with the “composite jack”. Even though both composite video and analog audio come in the same break-out cable on the WDTV, they are independent of each other, you can choose to connect either of them, it doesn’t affect the other.
In your case, if you can make use of the component video output, you don’t need to hook the yellow connector (composite video). So basically, you can use the analog audio connectors to send audio to the amp, and connect the optical audio to the HT. That will allow you to have surround sound on the HT and stereo sound on the amp, but probably not at the same time, as I don’t think the WDTV can have both outputs running at the same time.
If for any reason you’d like sometimes to listen to the WDTV output on both the HT and the other amp, the other option I mentioned on my previous post, is to hook both amps using the “zone 2” output of the amp that receives the analog output from the WDTV, not optical. That way you could listen to the stereo signal on both amps at the same time (when you switched to “stereo” in the WDTV preferences), or 5.1 on one of the amps (when switched to “digital”).