I talked to Dave Gordon of Audio Research at an event in Seattle and asked him about the change. He said there were two reasons you should upgrade: first, he thinks it improves the sound (he had just told one of his friends to send his back for the upgrade) and second, not only is the 5881 tube less expensive than the 2 6H30's but they are hard to keep matched during longterm use (don't have to keep 1 tube matched :)). I am going to send mine back in the nest several weeks.
