Hi, Chris!
Yes, the Orchestra Reference came with Ei KT90s. Though it was the best amplifier I encountered on my budget when I was shopping around, over time, I guess I grew bored with it. The sound was good, but there was a coldness in the midrange that kept me from remaining involved with the amp emotionally over time. Later, I tried AtmaSphere, Blue Circle, and Granite separates, and they were all fine - the Atmas and Granites being my favorites.
As the JOR was collecting dust, and Denis expressed interest, we agreed upon a deal to sell it to him. In discussing his sonic priorities, it seemed that the EL34 tubes were what we should try. We went with JJ Blue Glass E34L. Wow! What an improvement. The amp went from being very good sounding to absolutely beautiful sounding. The reduction in power required two clicks up on the volume control to produce the same loudness (actually, that's pretty much insignigificant), and the bass response was nowhere near as good. But, oh that midrange, incredible! Don't think I have yet heard better. Also, I must note, the imaging was also perhaps the best I have encountered - shocking, but superior to the Atma and Granite monos.
For fun, I also tried my JJ KT88 in it for a few songs. The bass and dynamics leapt forward greatly, and the midrange still seemed beautiful, though I didn't spend enough time with it to be sure how it compared to the EL34 tubes.
Yes, the DA60 can use EL34 tubes, as well as 6CA7, KT77, 6550, KT88, and KT90. I got it with Sovtek 6550, and while the amplifier sounded good with them, last Saturday I installed JJ Blue Glass KT88, and the performance improvement I have gotten is no less than stunning. The Sovteks just were inferior to the JJs in any area you wish to compare them. Along with trying some Sylvania 5751 after that, I'm amazed at how beautiful the amp sounds. The power, slam, and bass are more than I had hoped for. The midrange is also great, but as of yet, I have not fallen in love with it the way I did with the JOR running EL34. I'm not even sure it was as beautiful as I remember it as - you know how memories can sometimes grow stronger over time.
So, that being said, I am awaiting an octet of the newly released JJ KT77 tube, which is a premium EL34 variant. Part of me wonders why I just didn't go with the Blue Glass E34L, but I'd like to try these. At any rate, my dealer is going to let me know as soon as the KT77 arrive, and along the way, if I change my mind and want to go with the E34L, he'll have them on the shelf when I get there.
I'm not really sure that the DA60 can get much better, and I am not sure if I could live without the slam the KT88s are providing, but I guess once you experience that "to die for" midrange, you almost are willing to. So, I am chasing it via these JJ KT77. I'm also interested to see how much of a downgrade in power and bass the EL34 type tube gives in the DA60, though with those massive transformers and 8 output tubes, I can say that right now, I have plenty of power to give up.
Once they come in, and they are burned in for 100 hours or so, a bunch of us are getting together to have a tube shootout between the JJ Blue Glass KT88, JJ KT77, and a friend's 1960s Mullard EL34 XF1. Any Audiogoners who are interested are certainly welcome to come over.