Terrible Booms

Doesn't matter what speakers you use,or what footers or platforms.The bass waves are going to continue to cause the boom as they slam back and forth and up and down.To tame those waves you'll need to treat the front wall behind the speakers,especially the corners aggressively.8-10 inches of rockwool straddling the corners.Check GIK Acoustics site for more information and a free consultation.Here is a good site that explains room modes.http://www.sengpielaudio.com/calculator-roommodes.htm
Also adding two -four subwoofers will smooth those standing waves and room modes right out.Really!It's called "the swarm".
I have a less than optimal room myself and understanding and treating treating the room properly was a huge step forward.Adding two subs was another huge improvement,two more even better.If you really like your speakers do a little research first about acoustics and how to improve your space.

The floor won't resonate problematicaly if the bass waves are controlled.I have a "live" room myself.If the subwoofers(that fire towards the wall) are pulled away from the wall farther than 2 inches the floor and everything else resonates.You can always buy new speakers that don't go low enough to excite the room if that's what you prefer.Personally,I would never be happy only hearing just the upper bass notes.

That's good news!You were right about the structure of the floor being the problem.I live in an old house too,but not that old!I learned a lot from this thread.