I didnt find anything either when I searched for MXL.
But I have then found out that Musescore can export midi files from with CC1, or CC11, and then if I import them, I get the values ββfor either mod wheel, or expression. I did not know Musescore could do that, but after a few hours on google I found the answer.
It is one of my VSTi's (BBC Symphonic Orchestra) that uses mod wheel or expression.