It would be a good move for you to try Class A and/or tube equipment given your Zu. I tried a number of solid state Class A with my soul Superfly when I owned them, but I much preferred tube equipment with high efficiency drivers. And low watt also helps to maintain low noise. Some of my favorites with Zu included:
Oliver Sayes Korneff 45 Clone (4wpc)
Bottlehead Kaiju (300B, 9wpc) with upgraded caps and tubes
Atma-Sphere S-30 3.3 (10-30wpc depending on number output tubes used)
As with any Class A or tube, allow 30-60 min of warm up to sound their best. This doesn’t mean that the system sounds awful before the amp is warmed up, but most can detect an audible difference that brings along additional transparency/openness and dynamics when the amp reaches full heat. I don’t recommend wasting the energy to turn it on prior and come back 30-60 min later as it is just that - a waste of energy and time.
Yes, these units will incur more heat and run up your electrical bill. They aren’t by any means “green”. But with the size of your space, if your listening position is a good 8-9 feet or more from the amp, you probably won’t feel it too much from your listening position. The open space will likely not run up the temperature of the room. If the room were more like 3-5 meters, that would be a different story. But you will notice a bit of a bump in your electrical bill, probably by a couple of bucks each month, depending on how much the amplifier is on.
All worth it in my opinion, if it brings the sonic benefits you seek