You can use a std BBC RGB cable with the Einstein but you need to make a very simple mod internally.
You have to take the top off to set the output jumpers from YUV to RGB anyway..

Use a small piece of kynar wire and connect the centre pin of the 6pin din socket to the nearest +5V pickup point (use a meter to find it)

This upgrades the Einsteins socket to the same spec as the BBC machines...
No limiting resistor is needed as the Beeb scart cable has one already inline.

This is the setup I use with mine..