Heresy IV vs Zu DW6/Soul mk2

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.

I don’t want anyone to get me wrong. The Klipsch series are great speakers. The whole line up has something for everyone. There is something to be said for a historic company, having produced iconic speakers for so many years. I did like the sound of the Heresy’s. Dynamic, the complete opposite of boring. Great mid, nice open sound stage. And they were particularly good listening at low levels. Someone I talked to told me I didn’t give them enough time to really settle in, and maybe they are right.

I don’t think you would be at all disappointed bringing them home. 
 

A speaker that has peaked my curiosity is the Heretic line out of Montreal. High sensitivity. The Big coax, big box, series crossover. All those combined, should make for a dynamic presentation with a soundstage to match.

I own Cornwalls, and really like them! They’ve been heavily modded w Crites tweeters , crossovers and major internal bracing. I’m regularly amazed at how delicate these big boxes can sound. And of course, they can crank it out. Been wanting to pu a used pair of Heresy’s for fun so I can do some comparisons between the Klipschs. 
 

Sometimes, you just need a big box with big drivers.
 

I've had Heresy IIIs (Capitol Records version) for a few years and love the things. I tried a pair of IVs (figuring they would be better) and didn't like them at all although they're really well built...some upper mid frequency anomaly drove me nuts (the plastic midrange diaphragm on a re-designed horn is what I suspect is the culprit...the IIIs have a completely different titanium longer throat mid horn) so I sold them off. Same with ZU DWs...they sounded lame compared to the Heresy IIIs so back they went. The IIIs amaze me every day, and maybe just thrive on good gear in front...Schiit Freya preamp with an SEP tube or Pass XA 25 amp work perfectly in my rig. 

Forte IV has almost the same footprint as the Heresy, so if you can swing a few extra $$, I'd recommend them over the Heresy.  Sounded great w/175 wpc class AB amp and tube pre; even better w/30 wpc class A.  Don't let anybody sway you with the adage that "they're best w/low power tubes"; IMO not true at all.