After well over 200 hours of burn-in of the Weiss opamps I did my first focused listening test. The low-quality / distorted / unnatural midrange has come back. I could have sworn that issue was largely resolved by the Sparkos, but maybe I was misremembering it or I wasn't paying attention to midrange quality? Anyway it's pretty bad. Sounds sort of metallic, "buzz-y", which is why I want to call it a distorted sound. I switched to a $300 NAP200 clone just to make sure it wasn't something else in my chain -- nope, good quality midrange.
I HAVE to ask those of you who own this amp if you really can't hear this low-quality midrange? It's pretty obvious in vocals and horns.