http://www.dv247.com/en_GB/GBP/Palmer-PAN-16-DI-Box-19-8-Channel-passive/art-PAH0016411-000
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.
http://www.dv247.com/en_GB/GBP/Fame-Audio-DI-120-/art-PAH0012038-000
Whatever you choose in the end, important is that all inputs of DI box have a "Ground Lift".
