UI and Operation:
I really like the Crimson UI and HD screen - the saturated colors really pop and make album covers look beautiful. Performance is fast and responsive, too, though I think there are bugs: AK Connect is not detecting my NAS and I'm getting a weird error at the system update screen.
HPs - Low Impedance/Low-ish Sensitivity Planars:
DCA Stealth (23 ohms/87 db?) performs like I mentioned above (disappointing). Not many options I know, but I would look elsewhere if you want one device to power headphones like these on the go. The PA10 for some reason is able to drive this headphone much better, regardless of source device, but it needs a separate source.
Ultra and PA10 is a very nice paring here in pre-out mode. Using pre-out mode on Ultra into PA10, there does seem to be a headroom cap with volume maxed out on both devices - loud for me at ~95db. Ultra line-out to PA10 gets louder than pre-out but sound is more strained. Ultra headphone out by itself gets louder, but distorts in the bass around 105/150.
HPs - High impedance: ZMF Aeolus and HD6XX (300 ohms)- have lots of headroom and sound really good (clear and transparent sound) with no discernable noise across all gain levels. The Ultra gets plenty loud by itself with these headphones.
IEMs: Not my primary use case but the A12T's sound good out of the Ultra, though does not have that full, 3-D, expansive sound I get from other DAPs. Bass not quite as refined, either. I'm hearing slight noise sometimes when changing volume while tracks are playing, no big deal.
Ultra and PA10 on a desk would bring high performance in a small footprint - I think thanks to that Pre-out on the Ultra. Maybe this makes sense if you have limited space at home. I would not want to travel with both devices.
The Ultra could make sense depending on what headphones you have (obvs). However, speaking in terms of pure headphone drive, I don't know what this gives you over the Max.
The maximum volume and highest gain in class-A PA 10 100% corresponds to what volume and what gain in ULTRA?
How would you suggest I test this?