@hardrocker69 I am no expert but here is what I think. The Heresy's are super sensitive. The audiolab is pretty powerful. I am not saying they are a bad match but muted is not fun, it almost makes me think that there is something wrong with either the speakers or the amp. Maybe they are not hooked up correctly, it happened to me more than once. I would listen to each speaker separately. I would try bright and neutral music.
I have placed speakers in ways that they sounded terrible but never muted. Placement is the easiest and biggest mistake.
Experts here would suggest room treatment and different cables. I would definitely eliminate first whether it's the source, amp or the speakers that mess up the highs and mids. Both the amp and speakers are high end in my book, so you should expect to be wowed.