I've been fooling around with various material as well, I'm having a piece of granite made to size for use under my turntable, mostly because I already have a large piece of 1" thick granite when I had my kitchen re-done this past summer (chunk left over when they cut out the opening for my sink). My Oracle Delphi's three feet may make using footers a little difficult, but sounds like it's worth the effort. Have you tried marine-grade plywood? I found it made a noticable improvement under my CDP, softening the sound just a bit and making the digital "experience" a little more musical. Easy enough to paint to suit your tastes should you decide it makes any noticable improvements. On a related note, my local dealer gave me a Cambridge Audio isolation platform I haven't got around to trying yet, it's a metal platform (same box as they use for their outboard DAC I believe) and five round black balls that go under the platform. I intend on using this platform in my office system, under my Oracle Alexandria turntable. I'll play with this for a bit and leave a post as to the outcome.
Footers/Shelf Material
I am still on the shelf quest, trying Corian, Neuance and Maple Butchers Block (the latter is still to arrive, but is coming). The Neuance is still the best - the Corian less dynamic, slower and a little warmer. But I have also been trying lots of footers with these shelves, hoping for a magical combination. And I found one.. With hard shelves like Corian, glass, perspex, marble etc (including the Neuance) - (but definitely not for MDF), the best I have found is the E-A-R Large Isolation Feet, $3.25 each at the Parts Connection. With hard shelves all of the cones I have tried are way too peaky. Plain old hard rubber feet are muddy and smeered. Vynil feet in general are "zingy" and tend to hardness from the middle of the mid-range on up, and a bit smeered on down - and this includes Vibrapods. The Vibrapods are a bit too lively in the upper mids and not great with string tone, but are also not coherent from top to bottom (but are otherwise second-best to the E-A-R feet. But the E-A-R feet give you all the detail of the best of the other footers (cones, squishy feet etc) with NO peakiness, and fantastic solidity to images. They are an unfortunate shade of blue and look like a hard synthetic rubber, but do not have any of the fuzz and smeer that you get with hard rubber footers. More neutral overall than anything else, all the detail as you get with cones but with none of the peakiness, none of the smeer you get with rubber, vynil, or sorbothane. I like them. There are also small feet at $1 each, but my components are too heavy for them and they sound muddy and grey - but they might work with light components - they are used by Sonic Frontiers on all their better gear. Please note I do NOT recommend them if you use MDF shelves.