I agree with your husband that it is user error. I had the exact same problem with a Brother 1500S. After much practice and changing to a bigger needle I can do it OK. Until I'm tired. Once the thread starts fraying, I know I have to take a break. I'll be able to do it again in a little while. I just has to have something to do with the way I (and maybe you) are moving the quilt around.
And just for the record, I do use overlock serger thread often for FMQ. I realize it is against the rules, but I do it anyway.