So, you can get 1 rubber out of rubber wood using an extractor, but you can get much more out of it than that. You can use the transmutation table from Equivalent Exchange. Rubber wood has an EMC of 32, and you can trade it for sticky resin, which has an EMC of 24. Do this in mass quantity, and you get more sticky resin than you had rubber wood. you can then put the sticky resin in the extractor, and get 3 rubber from each, vs. the 1 you would have gotten by putting the rubber wood in the extractor.
It's a great way to more than triple the rubber you get from rubber wood!