I have a JCM900 SL-X 50w head and a 1960AX 4x12 cab,this is the reissue cab with the 25watt greenback celestions and checkered grill cloth.
Nice sounding ut the head is a little harsh compared to a JCM800 2203/2204 or a SLP1959 or 1987(plexi's).
Try using an EQ pedal this will reall boost the amps balls not to mention it can provide a clean boost.