Floor protection from spikes

No worries. The EBAY listing provides little useful information and you were not given direction here. Perhaps you can contact the vendor and change the order to 30 hardness. Even cutting a single 70 hardness puck into 4 pieces will be quite stiff.

The Herbies gliders are great and come in three different variants of brass, titanium and I believe stainless steel. I use them (brass) under the factory spikes of a pair of 160lb Wilson Sophias to great effect. Initially bought them just to ease the movement of the Sophias as I adjusted the sweet spot and removed them as that was achieved but was quick to put back as the improvement with them was quickly made apparent.  Enjoy the music

They also come in giant size (which you might want), and regular "cup" shape or with integral thread (lots of different size threads).

What method are you using to attach or put these items under such heavy speakers?    

No method, they are deep dished and with my speakers show no signs of slipping out of the dish as I slide and adjust the speakers across my hardwood flooring. The three variants of the sliders offer a different tone per say, I chose the brass as they were the cheapest and the original purchase was just to assist in the setup. I have also added their threaded jumbo sliders to a Led Balloon turntable stand replacing the pointed cones that came on it stock and love the results. Enjoy the music