Received the Phillips Miniwatt SQ E80CC tubes from my bud today, really like this tube in the Crack. It mates well with the 5998. Produced a small increase in gain. Probably the largest change in sound of any variant I have tried, all the rest seem very similar with small changes evident. Although this tube has high detail and resolution I don't find it cold and analytical at all. The Crack has an easier time driving the AKG K702s with this tube installed, and the HD650s really sound great. Thanks to Dr. Toobz for the tip.
Cheers,
Shawn