If so does it work by directly plugging into the Mic jack?
It does not work with the 6600 and the 1/8 mic input for both radios are wired the same. I am currently working on an adapter to make it work. I do not understand why Flex chose to wire the Mic jack the way they did. I do not believe it will work with any typically wired communications headset designed to plug into a computer headset/mic jack.
Rather than re-invent the wheel - I used the wiring as shown on the thread - https://community.flexradio.com/flexradio/topics/wiring-a-yamaha-cm500-headset-for-a-6400-m-or-6600-... - The SB-45 works great now.