The best isolation I have ever witnesses was Audiogon member folkfreak’s Herzan active isolation platform under his turntable. Very effective, and unfortunately very expensive.
Here's a real talking point: "low mass". My Music Reference RM-10 Mk.2 is a real nice little tube amp, but that niceness is not the result of it's low mass (it weighs only 12 lbs.). My RM-200 Mk.2 also sounds good, and it's a fairly hefty 52 lbs. I won't be selling it and buying a mass-market receiver from the "Golden Age Of High End Audio", the 70/80/90's. More silliness.
Low mass in a loudspeaker driver IS a factor in it's sound quality, for the obvious reason: That mass is moving. The faceplate and chassis of my EAR-Yoshino pre-amp are the heaviest (20 lbs.) of any I've owned, and it's the best sounding as well. I guess in spite of it's mass ;-) .