OK, I've resisted commenting for a long time.
They look like sh*t. Not kidding you here dude, whatever their function, the form spoils the whole intention.
Also, since you've 'cemented' the blocks together, you effectively have two 'joints' in the stand. I'm not surprised you're having issues with the bass.
Here's what I would do.
1. Set the speakers off the stand. Use silicon or rubber grommets available locally, rubber feet, anything. The speakers are being overdamped by the weight of the stands, some isolation will help.
2. Get a grinder from somewhere and refinish the block surfaces, and then use POP, wet sanding and acrylic emulsion to finish them off. Doesn't help anyone who's listening to them, but it looks a lot more presentable and professional.