I've had my Cornet2 up and running for a while now and can unequivocally say that all the people that claim the 12AU7 is important are correct. I've gone through a Chinese tester 12au7, a Philips ECC186, and both smooth and ribbed Telefunkens in this spot. The Chinese (no brand) tube was awful. The ECC186 had crystal clear highs, but was a bit too harsh for me. I was actually disappointed after the description that Tubeworld gave it. It was slightly stereophonic too. The two Telefunkens are similar to each other, but I'm enjoying the smooth plate version more than the ribbed.
I've settled on a Philips 12AX7 in the middle spot and a Brimar CV4004 on front. I've read on the forum that the middle 12AX7 has more impact than the last one, but I definitely prefer it there. I think it helps that it is such a quiet tube.
I'll be trying out a GZ32 rectifier tomorrow. I've been running a Tektronix branded (Mullard?) CY3 with some success.
Lastly, thanks to JH and everybody on the forum. Building and listening to the Cornet has been a hoot!