tough one man.Yes,I have and do use spikes,and yes there is an audible effect.But is it an improvement ?
A coin toss with some , a definate yes with other equipment.All my speakers and speaker stands are spiked top and bottom (reversed spikes on speaker stand tops)
I NEVER use spikes with tube gear,preferring instead some nice generic rubber feet or the bumpers off of doorstops.Same with line level solid state gear and DACs.
With my CD player I have tried taking off the factory feet and just putting a 12" bicycle tube under it,spikes in place of the original feet on a platform made up of a maple cutting board on top of a bicycle tue,spikes only,combinations of all the above and I STILL do not know what I prefer best.I will say internal chassis damping and some added mass are essential,the chassis and the metal covers on CD players are WAY too flimsy (at least at a rational dollar level)
The TNT "bullet spikes " are something i will try on a cold winter day when i am snowbound
All I am really saying is you really need to experiment with each individual piece of equipment,BUT NOT ALL AT ONCE,then make a decision on what YOU like.These tweaks are really a visual representation of the sound
I.E. -spikes,metal,tighten up a sloppy or too loose bass.A "hard" system might be toned down with "squishy" feet or even bubble wrap.
A slight "shudder (only way i can describe the actual sound)" might mean a total assault on the unit in question.A total approach from the internal chassis to the feet to the sub-stand and then the actual stand/rack,depends on how much bass power your system produces or how flimsy your home acoustical properies are.
Glad you asked huh ?