It sounds like hes having seizures from the toxin build up in his body if the enema has helped him so much, but this is a guess Im not a vet.
Here is a group I belong to that is very helpful with livershunt info.
http://pets.groups.yahoo.com/group/L...d_MVD_Support/
I would join and chat with others who experience the same thing.
This baby needs to have a bile acid test done ASAP
Your vet should be able to do it and its not a real pricey test.