You have room for more encounters than a d20 has in fact you can put both animal encounters and character and event encounters on the same table, rather than needing subtables for them, One of the problems with 2d6 is you get only 11 encounter possibilities, in d20 sometimes you could roll a d8+d12 and get more encounters, the more likely ones occur in the middle while the rarer one are toward the edges, and unlike 2d6, the probability curve has a flat area in the middle. d66 has an even probability distribution, so you are not stuck with a certain number of high and low probability encounters, you can arrange you probability distribution however you like with 36 equal probability choices.