I've had the SR1a since March but had been stuck using the Nu-prime while I waited for the AHB2 to ship (It was sold out worldwide at the time). With it, I found the SR1a extremely underwhelming in technicalities (especially in imaging) and tonality, only its speed impressed me. It was only after trying it with different amps that I experienced what the SR1a could do. The SR1a is extremely transparent, allowing me to hear the entire audio chain. With good upstream components, the SR1a becomes my favourite headphone (overtaking Susvara). Going on memory, it really does sound better than the HE-1. I suspect the HE-1 sounds as good as it does due to it's amp component as well.
I'm curious, what amps and upstream components have taken the SR1a to the top for you?