On my car, i have to change the menu to display "Kenwood" then the arrows control the HU, otherwise, like you say, it just moves thru the trip menu.
If you press the menu button on the wheel, what functions does it go thru?
On mine, i get the trip menu (MPG, range etc) Then the Setup Menu (configure the highline features etc) then Kenwood (Full control of the HU)