Increasing bass on floor standing speakers

Two suggestions:
1. Mount your floorstanders on isoacoustics Gaia feet. 2. Add (REL) subwoofers. 

Upgrade your speaker cables could make a big difference on bass. They did on mine. 

Did they ever sound strong? not any more?

Have you checked to see if the woofer’s cones and/or surrounds are in good shape? Look for pin holes, press in, check cone and surround stiffness: see if ’spring’ action feels good or kind of weak.

I have re-coned my 15" woofers (made in 1958) twice. They sound good, but I will be checking them soon, it’s been years.

I have to remove the back panel, then remove the driver from the front panel, check them out.

to cheer you up, from that album

Rocket Love, by Sophie Milman

https://www.youtube.com/watch?v=A2YO1DnRQBg

I used a polarity tester and the woofers are on the same phase. The tweeters were giving inconsistent results... One alternated with every pulse, the other was a little more random. I assume I wasn't using the app properly (I played through one phone connected to the amp and received with another. Used different frequencies and the L R fader.)
I'll rewire it with thicker internal wires when I know if I need to change any polarities.