Isolation Feet Recommendation for Equipment Rack

There are so many different ways to go but they all boil down to 
a) springs are best (without getting into expensive specialized stuff)
b) the best springs are damped
c) directly under a component has far more impact than under a rack.

You can easily make your own springs for your rack. First calculate your weight load per corner. Then search eBay for suitable springs. Nobsound are nice because they are compact and easily adjustable but you can find individual springs exactly what you want. I did this with my Moabs and some subs. Not that hard, just the search is time-consuming.

What you will find, everything between ordinary springs (Nobsound are just ordinary undamped springs) and Townshend is anywhere from a lot more expensive to hugely more expensive than springs, but not that much better. You do not in other words get your money's worth. For that you have to bite the bullet. Go big or go home, etc.

On a budget, to save money, I strongly recommend Nobsound under every component (but speakers, those really should be Pods, and yes totally worth it) EXCEPT the stand. The stand I would leave alone. Cones, spikes, whatever you want. Not because it won't help, but because it is so much less important that what you do directly beneath each component.

If you are still determined to do the rack, something to keep in mind- it is gonna sway. Mine even at 750lbs sways back and forth usually about a half an inch but sometimes more at the top, just from lightly touching it to cue a record. This motion is so slow (around 1Hz!) and smooth it affects nothing- except that you see it. Notice my rack is relatively squat- short, wide and deep. If yours is narrow or tall it will sway even more. Springs are best in terms of sound but sound isn't everything. You need to consider this. Because what it means is springs are best, but in this case really, really need to be damped, or the rack is gonna be swaying all the time! So either Pods, or plan on damping using something like Dave's foam inside the spring trick.

Honestly, looking at your system (which is pretty darn nice by the way) I would remove the spikes from the speaker stands and put them on Townshend Podiums. Yes I know you think that doesn't make sense. Because you haven't heard it. All this other stuff combined will pale in comparison. Then I would put as many of the other components as I could on Nobsound. The combination will elevate your entire system like you won't believe. 

Question.  If sonic vibration can cause degradation in the sound quality emanating from my turntable, how does placing the TT on springs solve the problem?  Would not the sonic vibration also be hitting the tonearm directly and causing the same issues regardless of the springs under the feet?  Answers appreciated.  

Right. Not only turntables, all our components have to contend with a plethora of vibration sources.

There are, at a minimum:

1. Vibrations generated within the component itself. Even zero moving parts components like amps and DACs generate a lot of vibration. With turntables there is at minimum motor, bearing, arm and cartridge. The cartridge alone generates so much vibration you can hear music coming right off the cartridge.

2. Mechanical environmental structural vibrations. This is everything from traffic outside, wind acting on trees and structures, that all adds together into seismic vibrations, mixed into which we have speakers mechanically transmitting vibration into the floor, and from there to walls, ceiling, rack, combining with seismic and into components.

3. Acoustic, the air, what we call sound. All the noise in the room. Hopefully mostly music but for this purpose it really does not matter it is all noise.

This is actually the least of the three, something you will appreciate if you ever put your speakers on Podiums and feel the difference. But acoustic energy being air affects different structures differently. Sound waves vary in length by frequency. A tweeter can be small, because the wavelength is very short. Tweeters will move at lower frequencies of course, you just won’t hear it. What happens is the pressure wave instead of being driven forward dissipates around the sides. A speaker cabinet is basically a means of preventing this. Without it, speaker in open air, loses all lower frequencies.

Now we have what we need to know to answer your question. The tone arm is so small the only frequencies that even "see" it are ultrasonic. Everything else goes right around it. Plus it is curved, makes it even harder for acoustic energy to go into the arm.

Turntable, bigger, is easier. Now it should be clear why a dust cover is so bad, great big thing practically designed to collect acoustic energy and channel it into the turntable.

Springs under turntables and other components don’t have much to do with acoustic energy. Mostly they isolate from environmental seismic vibrations. The biggest source usually being the component itself. Springs allow vibrations generated within the component to be dissipated within the component. This might not seem so great but it is a lot better than the alternative, which is vibrations travel beyond the component creating ringing in the rack and exciting all the other components until every component is causing every other component to ring in a great big smeary mess. This is the real reason springs work so well. They break that whole messy cycle.

@millercarbon

Thanks for that thoughtful answer.  Makes perfect sense that my Rega P8 does not come with any attached dust cover.  I have just ordered 3 Giai feet to try under the turntable.  Stunning that some of the isolation units for speakers cost more than some speakers I've owned.  I'm sure the law of diminishing returns applies to these.