I have to respectfully disagree with DefQon here. The PanAm is not a bad amp, and worth the price for what it delivers. I obviously don't have as much experience as others, but having these side by side it sems to me they all have strengths and weaknesses, but none of them I could call bad.
Bad synergy with some cans, yes, but great with others.
Anyhow, this just illustrates the subjectivity of perception in anything, really, not just in this hobby. Best way, try before you buy. Failing that, find opinions of people you trust and share musical tastes with. Emphasis on the shared musical taste for better reference methinks.
That's fine but put it bluntly it doesn't sound like you've owned or heard many headphone amp's at all, given that you've only had 3 that you've named.
I'm listening to them with the Burson Conductor, and I find them to be a great match, obviously the Soloist is a great choice if you don't want the built in DAC. The Conductor is supposed to be a pretty big improvement from the HA-160 from what I read, but I couldn't say for sure as I haven't heard it.
Any of the latest Burson offering is a big step up from the 160D, that amp was lifeless sounding with many headphones I tried them with before I went down the rabbit hole with electrostatic earspeakers.