Why not try one footer centered at the rear with 5 springs on it? There are manufacturers such as Esoteric that have only 3 factory installed footers under their disc players.
I’m just unsure and a little wary of the potential danger due to the 63 lbs weight of the unit. It has heavy duty cast-iron insulator feet which strongly support the component. The bottom plate at the rear middle may not be strong enough to be used as a support. Furthermore, there are air vents at the bottom which extend close to the rear of the unit. It’s a Class A amp.
If the component is less than 20 lbs I wouldn’t hesitate to use 3 footers as a support. My DAC is rather lightweight at 15 lbs, and 3 footers with 1 spring each may be too much.
I haven’t tried the second set of Nobsound on my DAC yet as I want to evaluate the performance of it on the amp first. I have to say, initial impressions have been very positive although the set up may not be fully optimized.