Something like the "Palmer PAN 16 DI-Box - 19" 8-Channel passive" would be a perfect solution. The "Millenium ADI 6 Aktive 6-way DI Box" is an alternative, but as active DI box it needs power.
You can get single DI boxes also in a two channel configuration. I can really recommend this one. It's not expensive and has no "name", but I have nothing negative to say about it. It's perfect for stereo keyboards.
Whatever you choose in the end, important is that all inputs of DI box have a "Ground Lift".