I have an A-100 and THX-789 for my desk, with the A-100 powering my Revel M16s (and JBL 530s before that) in near field. Source is an LG V30 Quad DAC sending Spotify HQ files. Through the speakers it sounds fantastic, with no perceptible hum or distortion and I've noticed no channel imbalance.
The headphone section really is a major reason people buy these, and I initially bought it for that as well as its speaker amping (and it's unique shape that fits better on my desk). The headphone output is definitely rounder and less clean than the THX-789 but that works well with brighter, high-impedance phones like the Beyerdynamic DT-1990. With the jumpers in it powers my Hifiman HE6SEs more effortlessly than the THX-789 but the noise floor/less-clean sound is more apparent. At this point I really only use the 789 for headphone listening (Hifiman HE6SE, HE-500, Focal Elegia).
Looks good on the desk too, with the 789 stacking nicely on top (I notice no heat issues in my application). Interestingly, the 789 will also pick up some hum from a nearby wireless phone charger if they're too close together but if the A-100 is picking it up it's inaudible.