I haven't tried the iHA6 or the Pietus Maximus, but here's my experience with a high impedance output amp and I hope it helps (long story short): I tried a few amps for my Verite, including some Violectrics and Feliks Euforia. Although the VO sounded great with all of them, the one that sounded best to my ears was the Euforia, but I didn't want to get into tubes yet, so I decided to go with a Vio V222
In the meantime, I discovered the small and inexpensive Beyerdynamic A20 due to some positive comments in the “amplifiers for ZMFs” thread and bought it just out of curiosity. I had read before about the benefits of high impedance output for ZMF dynamics and it really clicked when I first heard the A20/VO combo. The Beyer is a simple amplifier without any technicalities, but its 100ohm output brings a “tactility” to the music that is wonderful. Everything sounds fuller, meatier and there is a more natural resonance, without loosing control or detail. Guitar plucks sound bold and vivid, the decay of piano notes is a bit longer and more natural, violins sound fuller....
My theory is that less damping factor allows the driver to move more freely (it can “breathe” more easily) and that's something good for a driver as stiff, fast and detailed as the Verite's.
In any case, maybe it's just me and of course it's not night and day, but I think it's noticeable and, if possible, worth a try. Just to mention that all the SS amplifiers that ZMF sells on their website usually include an output impedance switch, so...maybe I'm wrong, but it says something.