If you're technically competent, or have someone else who is, and can refer them to this page, it lists a few changes that you can make to the organ, if you feel the need.
Drumkit mods
I found it annoying that the balance control operated the opposite way from what I expected. If you look at the rhythm buttons, there's icons of percussive instruments on them. The original wiring has it so if you pushed the balance control forward, it made the instruments on the bottom row louder, and vice versa. I wanted it to be that the direction of the balance control matched the instruments (push it in their direction to make them louder). So I broke the PCB traces leading to each end of the balance pot, and crossed them over.
It was also annoying how the tempo LED is completely out of my eyeline on the cheekblock left of the lower manual. So I mounted another LED central on the console above the stop rail. It's fed from a resistor between pin 60 (tempo LED) and on pin 59 (+5 volts) on the RHY board.
I found the bass drum was far too loud in comparison to other drumkit voices, so I increased R65 and R73 to 100K each on the RHY board.
I wanted to record the organ without drums, but be able to separately listen to them using them like a metronome. Or, record the organ with organ sounds and drum sounds on separate tracks. So I put the drum unit signals through switched jacks. This also allows a separate speaker system to be used for the drumkit from the main organ speakers. This output is post-expression pedal control. I also put a switch across the jack contacts so I could tap out the drumkit for recording on its own tracks, while still hearing the drumkit through the organs main speakers (essentially making the jacks unswitched). This was done by interrupting the signal from pins 1 and 2 on the RME board (drumkit into the RME board).