I wonder if the "9003" is a date code (1990 March).
For the pin-out, assuming that the pin-count is reasonably low, can you examing the amplifer PCB to derive the IC's pin-out ? That's how I would start...
There are many hits (audio related) for the following JRC opamps: NJM4556, NJM4560, NJM4565. Hopefully this lead (mostly the 'NJM' prefix) will help you to find the info you seek.
Ok guys,
i had another look at the device and of course i was looking for the wrong code - it is a NJM2041 Type. With that code i easily could find the datasheet.
Blinded by the obvious again ... thanks to all for setting me straight on this one.