You didn't say, but full depth, sanded-in-place, tongue-in-groove, hardwood floors are typically supported on wooden floor joists over a basement or crawl space. Wood flooring over a wood joist support system is very different from flooring over a concrete slab-on-grade. The wood joists will be more susceptible to vibrations than a floor supported over a slab-on-grade.
If your system is supported over wood joists, then an amplifier stand or support platform could be more effective than which blocks, or footers, you have directly under your amp. A platform may help spread the amplifier support over a larger area so that the support is derived directly from multiple joists while the four feet alone may be positioned on the flooring between joists. I suspect decoupling using compliant footers or springs may be more beneficial than coupling with spikes, for situations over a joist-supported wood floor. You may want to look into what has worked well for people with large speakers over joist-supported floors.
