I have a Janome6500 and it also gives me a warning when I put down my feed dogs but after the second or third time it allows me to FMQ. One time it wouldn't let me do it at all and then I saw that I had my machine in the wrong mode and on a decorative stitch.
So be sure you have your settings accurate before you try it. I'm not familiar with the MC9500 but if it sews straight stitches and zig zag, and your feed dogs go down, you should be able to FMQ.