Based on the serial # on the back of the unit, that is a JBL MC19 wired remote. This just the wired control unit. There should be a head unit buried back there somewhere as well.
Overall Size: 6 3/4W x 4"H
Fusion makes some models that are close to that form factor. You should be able to find the data sheets to get the rough cut and then compare with either newer JBL models or see if the Fusion will drop into that hole.