Calyxa Omphalos, who created the Elemental Hexagon deck, told me about this concept of using two tarot decks to do readings at Pantheacon. I thought I would give it a try recently, and I was very pleased with the results. I used the elemental hexagon deck and also Ray Buckland's alchemy deck. I interspeced the cards I laid down from the elemental hexagon deck with the alchemy cards I laid down, using the alchemy cards as connectors. What I found was that the connector cards naturally seemed to enhance the cards that were being used for the main reading. They provided complementary information that helped support the overall reading. It was also interesting to use two different sets of cards in conjunction with each other, particularly because with these cards it was as if I was forming specific equations (which could be really useful for using cards from the enchantment end of things).
I have to admit that just using the elemental hexagon deck has been very effective, but I also think its pretty to novel to use more than one deck for a reading, and what I liked about this approach is that it managed to fit into the theme of both decks, in terms of symbolic representation of processes the cards depict. I'd suggest that if possible it's a good idea to do this kind of reading/enchantment work with two sets of tarot cards that have complementary themes.
I'll report more as I continue to work with this rather novel approach.