Has anyone connected a MFJ-464 to the 6600m?

Hi John, I haven't used an MFJ-464, but the connections look pretty straight forward.

Paddles to Key In. Key Out to the Key jack of the Flex. The radio in, radio spkr and side tone jacks are not needed as the Flex produces side tone. PTT is not needed as the rig is keyed using the Key jack of the radio.

You would need the radio to be set with Iambic off and Breakin on:

You can also connect the keyer to pins 4 and 5 of the accessory socket if you also want a second set of paddles connected directly to the radio. I do this so that if my keyer (part of TeensyMaestro) ever fails, I can keep going using my backup paddles. This has never happened, but makes a good excuse to have yet another set of paddles at the operating position… :- )

If you are, by any chance, the JohnEin who lives in North Boulder, I would be more than happy to come over and help you to set it up if you like.