In response to a pm on HF:
The ZD plays well because of its euphony - a really luxurious ride. (OTL sound which has to be heard but hard to describe.) Yet at the same time, it's a very fast articulate sounding amp which does not compress the upper tips of the wave forms or smooth out the edges. Think good quality fast articulate solid-state treble and velvety midrange. You should be sure you like this honest treble quality. It's not going the blunt the edges of brighter headphones. But the luxurious bass and midrange more than make up for this for difficult brighter or wonky headphones. Seriously, think of a Mercedes AMG.
The Stratus is euphonic in a different way. In contrast to the ZD, its approach takes the edge off the treble (absolutely nothing wrong with this. My old BA also took this approach.) The Stratus is more intimate affair and carries with every note a certain warmth, while at the same time still being able to convey energy, attack, excitement, etc. It's a smaller GT type car which can take the turns hard, but it's also equipped with luxury amenities which make it tolerable for all sorts of roads (unlike a 400hp EVO which rides like shit on real roads). Hence why made the Audi S4 analogy.
