With ARC going to autobias, the tube matching issues will only be a problem for the existing user base. Everyone hears differently and prefers what they prefer. With this caveat, the kt150 has a superior sound signature to the 6550, kt88, kt90 and kt120. The shortcomings of each of those tubes have been overcome in the kt150. Let the flames begin....
I will again repeat, I want a civil and appropriate discussion. No flames here (from me) and hopefully none from anybody else. But then again, your post does smack of perhaps being a troll (-:
I am in the camp that believes that sound signatures are inevitable and a good thing in moderation. I never much liked the KT120 but there are 6550's, KT88's and KT90's that have a subtle "glow within" quality in the midrange that imo the KT150's lack. I happen to enjoy a slightly burnished midrange added to human voice, saxophone, and stringed instruments. The KT150's are unexcelled in slam/dynamics, frequency extension, and neutrality. Which brings to mind, why pay for the expense of tubes if it is only going to sound like solid state? The Ref6 preamp, as I stated in the deleted thread, lends a holographic, wide open and 3D soundstage that I have never heard in any solid state pre. It is a bit artificial but I am happy to have it.
On top of the KT150's solid state-like neutrality and expense, there is another glaring problem; only one manufacturer makes the tube and that manufacturer has demonstrated significant problems with quality control. Perhaps not only will someone influential at ARC read this post but Mike Matthews as well., Wishful thinking.