Well, i dont have any experience with the RB81, however my first instinct is to say heresy all the way. I just dont think the RB81 would be able to keep up to a Heresy. I think if you were able to do an A B test with both speakers the decision would become clear. Either way you will need a woofer for a HT surrounding either choice. If you can fit Heresy, i'd build around those, Three Heresy's across the front sound stage would be a killer setup with a good sub.
Now having said all that, If you build a system around the RB81, i think you would be happy with that too. There are lots of happy Reference users around which will chyme in. They might have more experience with the RB81's....