improving bass on large floorstanders....

Getting your speakers situated and leveled with spikes is essential. You can't hear whatever bass your speakers are capable of without them. Getting the speaker positions balanced between optimum soundstage and just-right room boundary bass reinforcement is essential. A high current amplifier certainly helps, as does turning the amp on for awhile to charge up the capacitors fully before playing music. For better bass also consider Transparent or MIT cable, though there are several that do bass well.

Like KR4 says, its the room. Start over with speaker placement. My favorite for proper bass response is the Sumiko master set method. Choose whichever works for you. I never found formulas of any kind to work for me. Good luck.

Tell us more about your system and room. What kind of floors are we talking here? That will be a consideration when considering spikes. If you are looking for tighter bass, you might want to look at your amp. Maybe an amp with a higher damping factor would help.

I'm anti spike having spiked for many years. I use Vibrapods under my floorstanding speakers (Silverline Preludes), although not my sub (REL Q150e)...it sits on felt pads just to keep it from scratching my floor. I might be nearly alone in this, but it all sounds great in my room with my impeccable taste , amazing ears, and humble demeanor.

Matching speaker bass output to room size and positioning of the speakers within the room boundaries should be your first priorities. Once optimized you can move to room treatments if warranted. Changing cables should be at the bottom of your "to do" list since (IMHO) 90% of the bass quantity and quality will be determined by the other factors.