Symposium Ulta Shelf under floor standing speakers - Any Thoughts ?

I agree with first posting, if you are considering this option I would look closely at the seismic podium. I spoke to the distributor in the US  as I have been looking at them for my 800D's. Cost about 3800 US (full retail) for the pair for the largest size.

The Ultras will certainly deliver a lot of vibration absorption (dissipation of energy as heat), but, you should at least experiment with the effects of raising your speaker that much higher off the floor.  If you cannot borrow a pair of Ultras, you might want to use wooden blocks or something to see if the extra height helps or hurts the sound and to see if adjustments to speaker placement can take care of any issues.

Other options include footers like those supplied by Stillpoint.  A local dealer really likes those footer under many of the floorstanding speakers they carry (Magico, Raidho, and Focal).  These things can be much more expensive than anything else mentioned here, but a lot of people swear by them.

I tried svelte shelves under my Opera Callas monitors, between the speaker and the stand.  It definitely "cleaned up" the sound, but ultimately, I preferred the speakers directly on the stands.  IMO, they took some of the warmth out of the sound.  I would imagine they would work well in a more boomy system that is lacking in bass definition, but as stated above, you really have to try it to see.  I think many people, in a search for detail and clarity, end up with thin-sounding systems that are difficult to listen to in the long term.  

I saw Peter's (owner of symposium) demo at the NY audio show back in 2003 and was very impressed.  (he hit a crowbar against a rod of metal and it rang like a telephone.  He hit the same rod with the same crowbar, but the rod was resting on a Fat Pad and the ring became a 'thud'.  I was sold.  I had the svelt shelves under my Sanders Stats (100 lb, 6 foot electrostatic speakers).  The immediately tidied thing up in the sound and made my wife very happy with the high hats down stairs no longer vibrating (unless I really blasted).  Had that for 4 years, so figured, what the heck, and I upgraded to the Ultras.  Tightened up the sound even more (can't imagine better) and I can blast as loud as I want and the high hats don't even wiggle.  I would never not have symposiums under my speakers.  They are a deal breaker for me.  (and Peter is awesome).