I bought a vertical SS rack some 15 years ago. I replaced the supplied selves with John Boos thick cutting boards and specialty audio boards made from violin wood, and tried a wide variety of pucks, cones... to isolate the shelves from the rack. For years I felt that the rack sitting between my speakers was messing with the sound stage. A couple months ago fell into a fantastic deal locally on a DIY table made with 5 x 2 x 2" thick solid maple that I fashioned into a horizontal shelf raised ~ 2ft above the floor. Words like; jaw dropping, magical come to mind. Yesterday I played Patricia Barber Modern Cool, MoFi hybrid SACD, which I have listened to many times on various system tweaks and changes. NEVER has it sounded so there there, and Ive seen her live a couple times
Recently I saw and advert for a multi-shelf horizontal rack made with sold maple for ~ $2100. If you can find a way- buy it
hth