Mass and vibration cancelling on top of CD player?

ZD. I put a heavy book on a marble tile (on a piece of heavy cloth to protect the player)(no cones) on my Lexicon RT-20 and have been "very" pleasantly surprised. I was using a very "average" CD-- Portrait of John Williams (MK37791)-- as my test.
There had been a very minor degree of harshness in the higher treble notes that I had attributed to being the sound of his guitar (I should have known better-John's ear would probably be as sensitive as that the most ardent audiophile). With the added mass the harshness was gone! The CD all the more enjoyable. Without question this was due to "damping of the vibration to the player caused by the rotating disc" as there is absolutely zero vibration transmitted from the speakers to the player.
The added musicality on strings, as well as orchestral, is very much appreciated. I have exceptional separate ac isolation/conditioning for my pre, amp and the RT-20 and I probably am in a better position to evaluate this effect than most as I'm also using reference Spectral & MIT products. There is no question of the result-so I guess this confirms why the serious attention paid to ridgidity and mass among the high end players. I of course will now look to further avenues for sound improvement as I am not able to buy an Esoteric, Wadia, Spectral or other top CD or combo player at this time.
Any suggestions on my next experiment?

Making the chassis rigid doesn't prevent the disc from vibrating, which in and if itself is not too good for the sound. One way to ameliorate disc vibration and flutter is to obtain absolute level of the disc while spinning. Not as easy as it sounds.

My transport is level, but that is not as critical in my setup, as I use a Pioneer stable platter transport which clamps the disc.

I use low weight cast iron barbell weights (2.5, 5 lbs) to which I glued 1/8" cork on underside.

I don't understand why dead level is so important. It doesn't seem to matter to a gyroscope? I like the cork idea. Probably could serve more than 1 function.