Decoupling speakers that actually vibrate, and which can vibrate a floor, from the floor, I get. The effects are actually measurable.
Spring footers under a dac seem about as necessary as wings on a pig. Unless you are perhaps on a ship in a storm, it doesn't make any sense to me. Under any normal circumstances, there is no reason whatsoever to expect it to change the sound. No more than it would help my computer run it's software better.
But...I'll leave it at that.