It may sound dumb, but I would swap the DAC... If a particular oscillator just needs one bit that isn't needed by any of the other oscillators and it's bad, by coincidence, you can have them fail. It wouldn't show up on the others, because it isn't needed. I saw this on a Polaris, and it took way too much time to find it. Can't hurt to try it. Same DAC as an OB8...
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Sent from my iPad