BBBB... sounds like you are pretty much on it. Just connect the E60 to the Duet's inputs, and route Logic's outputs to the speakers.

If you are doing this live, latency might be a small issue, so listen to the E60 while you play using headphones outs on the E60.

Alternatively, if not singing or anything else, use the E60's Recorder to record the performance, then play it back and record using the Duet. Latency won't be an issue this way, plus, if you have a Part that sticks out too much, you can use the Song Mixer to rebalance the sounds (many of us tend to make the lead sounds a bit too loud) before you record to audio...