Hi and welcome,
Do you really need MMC for this? I would recommend to change the HW settings so it sends common MIDI CC and use Cubase Generic Remote Device to map it to the functions you want to use.
The only one advantage of using MMC I can see is, that the buttons could illuminate when you press the Record/Play in Cubase (not on the HW). But Mackie Control protocol is much more suitable for this.