Having trouble reducing the vibrations on my turntable setup

Any shelf will vibrate at a certain frequency. Depending upon that frequency, there will be regularly spaced nodes that remain stationary even while the shelf is energized and vibrating. If you can locate those stationary nodes and place the points of your cones directly on those areas, then the cones can provide isolation. But it's very tricky to locate those nodes.  

Oh, it's not tricky at all- they are all over the place! Problem is, they move around depending on the frequency. That's not the worst of it. Look how many there are in the midrange frequencies where we are most sensitive! 
https://youtu.be/WmwnN_T_wW8?t=40

Springs bounce and resonate. Townshend controls this with an ingenious air resistance damper. Without knowing what IsoAcoustics is doing it is hard to say. Probably a solid mass under the Podiums will be best.  But you will just have to try both ways to know for sure. 

Spikes unscrew. If they are the same thread size and pitch as Pods you luck out. Get a stud and screw the Pods on in place of the spikes. Pods are threaded to allow the top to be turned for height adjustment. Makes turntable leveling a breeze. You could use them that way. At 50 lbs your turntable will be stable on them. But you could also screw them together and still have the height adjustment. Whichever you prefer. Just pointing out options here.

Sorbothane, occasionally you find some place it does what you want. In general though it is so soft it sucks the life right out of the music. A much better material is fO.q tape. This used in the right places will make a huge improvement. But it works on micro- to nano-vibrations primarily midrange and up. The problems you are hearing are much larger amplitude/lower frequency. 

Ditch the spikes altogether. I tried a whole bunch of em, used BDR Cones for years. Pods beat them all. No agonizing is it really better, or its better this way but what about that? None of that. Not even close.

The problem is the Clearaudio uses spikes, which is not very good (read, any) isolation from the Delos butcher block. The solution is replace the spikes with three Townshend Pods. Your turntable at 24kg would use 3 Pods, 8kg per Pod, that would be the size C Pods, green on the chart. http://www.townshendaudio.com/hi-fi-home-cinema-equipment-vibration-isolation/seismic-isolation-pods... These are the same ones I use under my turntable, and the improvement is obvious. Besides dramatically lowering the noise floor there is a distinct improvement in clarity and much more tonal or harmonic truth to instruments. Bass is greatly extended and tighter. Jut a huge improvement.

Two other guys with similar issues PM’d me and took my advice, with the same great results. I know that’s the right size from doing mine, but never hurts to give John Hannant a call, just be aware the Pods work just as good under amps too and so it may prove to be an expensive call. But then again to transform your system (which it will, it has mine) well worth it.

https://www.audiogon.com/listings/lisa7140-townshend-audio-seismic-isolation-pods-set-of-4-sizes-a-b...