Just found the JVC box. It's a CS-J1720X. 165mm with a depth of 44mm. That's actually too thick, so I think 40mm is the maximum allowed (hence the filling need)
@@blaap Ahh, its undersized then. The correct size for that hole is the 17.1cm/6.5". It obviously fit but its slightly undersized. No biggie, it worked. :)