Arthur, thank you for your perspective!
All I can say is that "if it sounds right, it is right." And, in my case, these 5751 definitely sound right. It's funny because I bought them from a local guy, and he has thousands of tubes, and didn't seem as if he felt they were anything special. But, I guess he's never really spent a lot of time with the 5751. I told him I was trying them based on the claims of some that a 5751 can outdo a 12AX7, which he chortled at. He said, "You should try a good 12AX7." When I told him I had the Mullards, he said, "Well, I guess you can always have these as a spare or sell them or whatever..." Anyhow, they were not better in every area (weak bass) initially, but after about 3 hours, it was pretty clear they weren't ever coming out.
Do you have the same feelings in your CJ regarding the 5751? If so, just do what you know is right.
Regarding the DA30, I'm wondering just how modified it is? I believe I am going to relist it at a lower price, this week, as it seems as if a going through by Avi Brand might improve it significantly as was the case of my DA60. I wasn't sure what the actual market value of it was, as you see SO few of them come up, but I tried to scale it on what an Orchestra/JOR trades for. After the past couple of days, I'm not sure I could sell it in good conscience at what I listed it for. I want to discuss it with Avi to see if I could get a ballpark on what he would be interested in getting it together for the new owner for.