Can the S8 subwoofer be used with the A2 desktop speakers? I don't see any audio outputs on the rear of the A2 speakers?

With the original A2s (not the A2+ model), there are two ways to connect a powered subwoofer to them. The S8 has two inputs and an output, so you could send the audio signal into the subwoofer from your source, and then use the output to connect to the A2s. The other option would be to send the audio signal from your source into the A2s, and then use the opposite connection, meaning the input that is not being used, as an output to connect to the input on your subwoofer. Both inputs on the A2s will act as outputs when audio is sent into either the A or B input; this simply means that if you're sending audio to the mini-stereo input of your A2s, the RCA input will actually output to the subwoofer.