I used the variable loudness on my Mcintosh 4100 on my office rig. Last week the Mac got replaced by a new class d integrated. There's no loudness button on the Fosi amp and I don't feel that one is needed as there's more bass running flat than I got from the vintage Mac using the loudness.

— once told me a long time ago that using the LOUDNESS button will incur the ultimate wrath of the Great Audio Gods. And those Gods will banish you from the halls of audiophile Valhalla.

(but I can adjust the gain to the woofers and sub independently....I just usually live it set)