I am very satisfied with mt SX900 for all of the above reasons. As far as As the two control knobs lock is concerned,I did what I used to have to do with my KN7000. I set the two knobs on balance and keyboard volume,checked the parameter,and re-saved an existing registration. I then unchecked it so it so it was no longer involved in the save function. So far,after many many power on's and registrations, it has not changed from the original assignment.
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pa4X 76 ,SX900, Audya 76,Yamaha S970 , vArranger, Hammond SK1, Ketron SD40, Centerpoint Space Station, Bose compact