Multiple headphones on one computer

At my workplace we pair program and sometimes need to get on a call with a remote team member. We also have quite a noisy office. We have USB headsets for these reasons. We, of course, use macs.

In addition to the remote calls it would be great fun to be able to have music playing through both people's headsets and be able to talk over it. So some sort of ducking would be useful.

We've tried creating an aggregate device as described here but it only sends audio from one mic, and you can't hear yourself talking. So unless you know some setting tweak we don't, an aggregate device won't work.

I'm very close to creating my own utility at this point, but before I dive in and hurt my brain learning OSX audio, does anyone know something that will achieve what I want?

I haven't tried this, but if you're willing to experiment:

Try using (no joke) Garageband with your aggregated device setup. No need to hit the record button, but you can use the monitor function to hear yourself speak. And since it presumably knows what to do with both mics, you might both be able to speak.

You may also use LineIn to be able to hear yourself speak. And finally, soundflower may be useful if you need to shuttle audio from one app to another before making it to your headphones... like say background music from iTunes or whatever.

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Update from OP:

Thanks, I ended up going with something based on the ideas in your post but developed the solution on my own. Here it is: pivotallabs.com/ultimate-headphone-pairing