"It scales better with a proper amp" doesn't count if you're looking at the V30, bc in this case the V30 is just the source.
Sometimes (very often) people messing with higher volume level = better sound.
But that isn't the case.
The HIM mode is just higher output to the earphones.
There's no other improvement.
Whit that said, someone may like the sound presentation of the V30, and someone prefer a warmer tonality.
This can be achieved by connecting the V30 via USB to a dedicated Dac/amp.
It all comes down to your own preferences.
I can listen to my Era-1 out of the V30 with HIM fairly loud, but it isn't pleasant anymore.
While listening to a proper Dac/amp like R-28 or the Mojo, the sound of the Era-1 is more pleasant to me, even if the volume isn't on par with the V30.
One has to keep in mind that the V30 has a very detailed and "brilliant" sound presentation which works best with warmer tuned headphones, imo.
I'm curious about your findings using different adapters in between, nonetheless.
It's obvious that everyone has to explore the different behaviors for him(her)self in this hobby.
No fault on this.