1750 address conflicts?

[commodorejohn]

I have an SFX Sound Expander cartridge for my 128, but I also have a 1750 REU. I'd like to use them both, which should work fine as the Sound Expander has a pass-through, except that the Sound Expander's registers for the stupid piano attachment conflict with the REU registers. I've been informed that one of the jumpers on the 1750 can be cut and a switch installed to change the REU register base address, but I have a couple questions.

First, I've been told that one cuts jumper J2 to do this, but Googling around it seems that one's actually related to REU size. Which jumper is the one I need to cut, and where is it on the board?

Second, what is the new address for the REU registers?

Third, is there a way to modify the Sound Expander to just remove the piano registers?

Thanks!