Well, time for my 24 hour update. The ALO-780 have 123 hours on them now.
I do believe the treble has calmed down a little. But, with the re-cabled Ultrasone HFI780 I've been searching for amp synergy, and having found it can be some of it. All I know is that it doesn't bother me at all tonight, but there is no lack of treble either.
They didn't suddenly turn dull or anything, no dramatic changes. But, clapping on Jazz at the Pawnshop sounds quite real, and soundstage has opened up further. They still have a forward and not distant presentation, but the instruments don't sound as close together as before. Saxophones are much more natural and balanced with the burn-in and amp/tube synergy. No details are missing, and they sound best that they ever have.
As previously posted, I first found the DarkVoice 336i with Sylvania VT-231 ($60) in front and Tung Sol 5998 ($30) in the back is best for home amp, keeping the sound stage as big as possible, while taming the bright treble.
Tonight I spent a couple of hours swapping opamps in the iBasso D1 to see what suited the HFI780 best. I ended up with:
AD743x2 in the LR with a 2:1 adapter (the AD797 were very close), and the
LMH6643 in the buffers (instead of the AD8397 which was a little harsh), and the
LTC6241HV in the DAC (instead of LT6234 which was brighter).
This D1 opamp combo seems fantastic with the HFI780, although the DAC might still need a little taming. But soundstage depth is improved, and the frequency balance seems just right, while everything is very transparent. No details are lost with these opamps either, and they will play as loud as I need them to. It sounds very similar to the DarkVoice 336i now
HiFlight has been recommending I try some of these opamps for a while, and now I'm sorry I didn't try it sooner.
When skipping the iBasso DAC and using my Headstage USB DAC, the sound is wonderfully transparent, natural and full without any excessive brightness. The original opamp selections were optimal for my Grado RS-2 with APS V3 cable, Denon D2000 with APS v2 cable, HD600 with APS v3 cable, and Edition 9/Proline 2500. I will try all those other headphones with these opamps during the day Wednesday sometime.
So, next is to try more opamps in the DAC - I have left over OPA2111, AD746, AD823, LT1364, LM4562 (2), LME49720NA (2), AD8397 (2), and AD8066, AD8616, AD8656. Based on previous recent posts, I'm thinking the LM4562 will be the next one to try.