What you are trying to do is fix a small mass to a much larger one to drain away excess vibrational energy, to dampen resonance. It is the exact same principle you use when you fix a cartridge to a tonearm. Ideally you would bolt the speakers to the floor and I have seen people do this. The problem is the mass of your house is not solid. It vibrates also. Here a concrete floor is also a big plus but an option many of us do not have. After bolts spikes are the next best thing. Both subwoofers and main speakers should be fixed although it is more important for subwoofers. Putting speakers on isolation springs is an odd thing to do for two reasons. This allows the speaker to vibrate itself silly and the floor is going to vibrate just the same from the acoustic energy released by the speakers. So, if you want the ultimate, bolt your speakers to a concrete floor.
Does a Subwoofer Make Spiking Redundant?
I just added a REL T5/x to my system, and a question rises up from the depths of my ignorance: Does a subwoofer do the thing spiking speakers is supposed to do? Does a subwoofer make spikes redundant, or do they work at cross-purposes? If it's relevant, I've got the spikes on Herbie's Audio Lab puckies, on a (thinly) carpeted floor.