Setting aside the debate as to whether loudness buttons should be used, which amp has the best loudness button you've heard? I'll start with my vintage Sansui AU-666. I was never super impressed with the amp on other speakers, but I hooked it up to my Zu Soul Superfly speakers (using lampcord, of course!), flipped the Loudness switch at normal listening volume (~80db) and it sounded like a subwoofer was added to my system. My Superflys went deeper than I thought they were capable of going, yet the bass was not muddy or bloated. The effect was much more impressive than simply turning up the Bass knob, which just made the bass sound badly EQ'd by comparison. I honestly didn't hear much difference in the treble, but with the bass response I didn't care. What the sound might've lacked in accuracy with Loudness engaged, it more than made up for in fun factor! Let's hear your Loudness Love Letters!