JM Audio XTC open.

Little Fox is a great amp, not as neutral as the V550 (warmer and a touch rolled off on the high end) but I think I like it the best of the three. The Aune S17 Pro is great for the price, but lacks the driving power of the other two. 1266 TC clipping the amp even on high gain.

The best headphone on the market under $1000 right now. Beats a lot over $1000 as well.

Yes, both. Don't get the Alcantara pads, they muffle the sound too much. Leather is fine, but I prefer my current pads which are the Dekoni Sheepskin TH900 pads.

Both those are high current amps. So just looking at the output watts doesn't tell the full story. They are more powful than the number of watts would indicate.

Gustard A26 currently, I think 5V output balanced from memory?

I also have a Little Fox on the way. I can compare with the Aune S17 Pro and Violectric V550 Pro.

Only go with the Denon if you absolutely need closed-back isolation. The TH900 does leak sound, but IMO it's a tier (or two) above in sound quality.

To comment on temps. My unit is usually sitting at mid-50s, 54-56C usually. That's living in the hot part of Australia, with ambient temperature ranging between 23-28C in my room. I haven't seen it go above 60 even in 100mA high gain, volume near max with my 1266 TC.

Disclaimer: I may be half deaf due to too many concerts without ear plugs.. It definitely has 'enough' power to get them loud, but it's definitely not the best or most ideal amp for those few headphones: 1266, HE6, Tungsten, Susvara.

The volume does jump at step 56, but not a big deal. Unfortunately, this amp is not really ideal for my 1266 TC and (I assume) HE6/se and Susavara are a no-go. Clipping and distortion in low gain and with high gain, I'm at step 60 out of 63. My Monolith Liquid Platinum does a much better job...

I just received my amp not long ago. There is no amp I am aware of that sounds this good for this little money. It does run quite warm yes, but not hot I wouldn't say. Reliability is questionable though, only time will tell.

Open, warm, bassy, light on the head? Look into a JM Audio XTC open.

From your list, I would pick either the Focal Clear OG or LCD-X maybe. Also look into a used Fostex TH900 or E-MU Teak. I haven't heard the 109 though.

LTA MZ3 would be a good pick. I've also tried the HM1 and the Cayin HA 300MK2 which also sounded really nice. I'd lean towards a tube amp for the Utopia.