Price in review summary includes the tube upgrade.   This is a pretty limited comparison. I relied on the reviews of others before deciding to try a Mullard/Holland GZ34 in place of my stock Sovtek 5U4G in my stock Woo Audio WA6. (I should have noted the name of the Head-Fi.org: Headphones, iPod earphones, portable audio, MP3 players, high-end audio member that compared about eight rectifier and came up with the GZ34. Buddy, whoever you are, I owe you a beer. Well, I'm amazed that an amp that I loved so much could be improved so much. The new...