It's no secret that the Mainline is bliss with the 300 ohm Sennheisers in high impedance mode and delivers excellent performance to all cans in low impedance mode. Discussions either seem to lean towards other high impedance headphones, like Beyerdynamic/ZMF, or the Audeze products. This makes sense as in my experience (which does not include any Audeze), hungry planars like the Hifiman Arya aren't at their best with the Mainline. To be clear, I wasn't disappointed with the Arya/Mainline necessarily, it just didn't quite match as well.
I have also heard Hedd recommend "at least 1 watt" of power to make them sing. I was expecting similar or worse results as the Arya with the Heddphone/Mainline combo. Holy cow! Was I wrong!?! Yes, I was wrong. The Heddphone is glorious on the Mainline in low impedance mode. It has the juice to light them up and just enough gain to pull the minute details out of quiet classical passages.