You 18" dish with the old dual LNB is compatible. Not the superdish. The internal workings of the LNB are different on that one. That is why it is not compatible.
If you have 18" E* dish aimed at 61 (old E* HD & Internation location), then you can connect it directly to Voom without any changes. That is what I did with my E* dish. It works great.