Low and Medium gain both have lowest distortion possible. If you reduce dac volume you lose dynamic range though.
Tldr just use low gain if its loud enough.
PS: my Harmonicdyne Zeus are already pretty loud at low gain 9 a clock, thats when you can actually turn down dac a bit so you dont run...
I already mentioned why i think thats a bad idea.
1. No way the amp Amir got was a release candidate, but a prototype.
2. Free marketing and hype by Amir for a product which is not ready yet.
3. Preorders are a evil thing and have no advantage at all for the customer