How important is the rack you use for your components

prof is completely correct

Sure, "let your ears be your guide."  But ONLY your ears, not your expectation bias

so, do blind testing

As with cables, the more refined your gear, the more difference a quality audio rack makes. That is just my personal experience and therefor it is just one anecdotal data point that is infinitesimally significant. I went from an el-cheapo threaded rebar and mdf shelf to a Symposium Osiris Ultimate and there were huge benefits. The most obvious-a hum problem I had due to my Manley Steelhead picking up MFI/RFI vanished. Peter of Symposium touts the Osiris as having a Faraday Cage design implemented into the design principal. I was skeptical and bought it for the resonance control. Now, well hearing-or not hearing-is believing.