Help me salvage my rack

You can go the route suggested by Edle, or try a device like an innertube or similar inflatable rubber bladder under each component to act as an isolation device (one of our NJ Audio Society members has demonstrated conclusively to me the effectiveness of this type of isolation, which he does on a more complex level with silicone and air in the tubes and a sand/lead filled base). Vibrapods would also be a cheap tweak that might work in this case. You can always use devices to "tune" your resonances, although in this case I'd think isolation from the glass may be the better alternative if it's impractical to change the shelves. Does Sanus make replacement shelves in different materials? Maybe they, or your dealer, would be willing to arrange a trade?

To try something different you should be able to pick up a couple of MDF shelves cut to size for $5 or so at your local lumber yard. For starters without geting into upturned spikes, specialty soft footers and the like try isolating the MDF shelves from the stand with speaker tack, small pieces of a mouse pad, maybe brass nuts (the ones with round ends) and, you know, try out hard and soft footers that are readily available. I would also suggest that you take a look at the "shelf material" and "isolation" threads at this site for more advanced ideas. My suggestion is just an under $10 one that will allow you to get away from the glass in order to see what will happen and is not by any means intended to be an end all solution.

Try a lightweight isolation/damping platform like the Neuance shelf, on MDF if necessary, for a more coherent sound than air bladders. Good luck.