I can't speak for the Zu, but I have the Heresy IV and have not found them to be fatiguing at all. It's hard for me to think how another speaker, other than another Klipsch Heritage like the Forte IV, could sound better for live presentation.
Also consider the following: the Heresy maintain a dynamism and "live feel" even at LOW listening levels, and moderate levels... That's one thing that really impresses me about them; I usually listen at low-ish levels and I'm continually taken aback by how fresh and impactful they sound.
That said, are they my "lifetime" speakers after a lifetime of listening through the "linear sound" of Epi 100s...? Maybe not, and I'm going to give the Q Acoustics Concept 50 a try, see what I like better as my "forever" speaker... but I do not regret my Heresy purchase and they have really brought a lot of engagement and they are addictive such that I might not be able to let them go and could see "rotating" them in from for part of each year just to freshen things up a bit, even if I do ultimately settle on the Concept 50 as my primary.