The M22 is magnetically shielded, so its magnets will not affect the sub, and vice versa. The only problem I see putting speaker on a subwoofer is that the sub can cause unwanted vibrations in the M22's cabinet, which can in turn affect the sound.

Also, there's no problem running your speaker (or any) cables right next to the subwoofer. When it comes to magnetic fields and wires, you only really need to worry if the magnet is moving in relation to the wire.