I have a pair of UFOs that I use as balanced monoblocks and I got them with stepped attenuators. Mostly because it is the easiest way to ensure both are at the same level (even though it turns out I usually have them wide open) but also cuz I figured in a amp where everything matters a discrete resistor has to be better than a pot. But it isn't like I've ever auditioned volume control options so JMO, YMMV ETC.

I do not have volume controls on my SE84UFO25.  I am not sure where Steve fixed them, but most probably, 80-90% of full volume.  I control the volume from the pre or the DAC if I go direct...