glass shelves under components?

I have a Bello stereo/TV stand for my components which are Muse nine sig DVD/CD player, Audio Note Soro SE amp. I have these on brass cones which sit on the glass shelves. The sound had an edge to it until I put some very thin rubber between the point of the cones and the shelf and the sound warmed up to an amazing degree.

My question is: where, on a sound quality list, does glass fall? I presume it is one of the worst materials you could have under your components, and something like wood works better, but this unit worked nicely with my TV etc. Can isolation devices overcome the sound I get to an even greater degree or should I buy a new shelf system?
My preference for most effective electronics isolation is to use sorbothane directly between the component and the shelf. I ditched the cones long ago - they are metal and metal transmits high frequency vibrations from shelves. Glass would be a worse case scenero. If you want to try DIY try making some sandwich footers consisting of one layer of soft wood, one layer of sorbothane, and the last layer of hard wood. Its probably over kill but it might look better than just sorbothane pucks etc. If you want you could still use the glass shelf in lieu of the hardwood as support, but covered with sorbothane (partially or totally) and put a second soft wood shelf directly under your component. FWIW.
There are very few absolutes when it comes to shelves, footers, etc. It is very system dependent. Ask enough people and you will get as many answers as there are possible shelving systems.

You get "Glass would be a worse case scenero" but Naim makes a very highly regarded rack that uses glass shelves as do others.

Sorry, you will have to experiment.
Try Herbie's Audio Lab Tenderfoot or Iso-Cup footers between your equipment and your glass shelves. I've had very good results with these in a similar situation with a Sound Organisation rack with glass shelves. I may eventually replace the glass with maple shelves, but for now Herbie's footers seem to be the best solution. I've used them under digital sources and amplification equipment including Audio Note. You can find them at: Herbie's Audio Lab Footers
Glass is also used for LP platters, where resonance can be a big problem...
It is the implementation that counts.
All my racks (cheap sand filled metal and glass) have glass shelves.
I used sorbothane-like mats (again, cheap.. chemistry 7mm thick experiment placemats same material as bottle stoppers.. I got super cheap at American Science and Surplus..) that I cut into squares. some full size component, some 4" square. some 2" square, and experimented.
Agree that often gless shelves do benefit from a rubber energy absorber between the component and the shelf.
I had a glass shelf rack at one time and on the advice of a friend tried a very simple solution that worked for me. I purchased some 12" bicycle inner tubes at Wal Mart, one for each component. I inflated them so they would slightly flex under the weight of each component and placed them between the shelf and component. Experiment with the amount of inflation and placement till the component sits level. It was ridiculously inexpensive and worked quite well.
Glass may look great but it creates many sonic problems.
Try putting a sound absorbent board under a unit. Very inexpensive is something that Tandy Leather carries. It is called 'Poundo Board'. A 12" x 24" piece sells for about $11.
While its clolor is red, it works wonders.
Do like I did, get some custom made acrylic shelves. 1/2" acrylic that is 19" x 20" ran about $210 total for 4 shelves. That's $55.00 each with a polished front edge. You could also get 3/4" thick, that ran about $70.00 per shelf. Inexpensive compared to some isolation devices that would have to be put under each component.
thanks to all for your responses