Speaker outriggers

https://www.parts-express.com/Dayton-Audio-DSS6-BK-Black-Spike-Set-4-Pcs.-240-694
Or these look to be nicely made adjustable spikes 

Those will be worse in every way than whatever you have now. What will solve your problem and sound hugely batter are Townshend Podiums. Unfortunately you don't want to spend money, even though this will be like a whole speaker upgrade. Huge improvement. But not cheap. 

Cheap are Nobsound springs. Same $30 you are prepared to spend but miles better sonically, you will be surprised how much better. 

If cost is a factor though I have to wonder why you would bother. Your entire problem is using four cones on an uneven concrete floor. Why? Three points define a plane! Remove one, move another, use three instead of four. Problem solved.

@jmphotography ,
I take it your floor isn't level, hence the need to add a washer, is that correct?
If so, I would look at something at Herbie's, as it should be in your budget.
https://herbiesaudiolab.com/collections/loudspeaker-rack-decoupling-and-isolation
Actually, I would call them to get the best information on what you should get.

Though I will second Townshend Audio products, they are very effective, but very expensive. I use them on my components to great effect.
Bob

@millercarbon the reason I did not want to spend a lot is I plan on purchasing new speakers later this year. Looking at SF Sonetto V. I was going to invest in the GAIA II and use them on the B&W and then just transfer them to the new speakers once I buy them. The Podiums are amazing I’m sure, but 2600 will give me a nice down payment on new speakers.

@gbnrbob it’s pretty level, it’s new construction, but it’s a concrete slab so it’s not perfect. The one speaker sits rock solid with no shims. The other needs just a really thin metal washer between the spike and cabinet the get it perfect. I was checking out the Herbie’s stuff. Thanks

My listening room is ~ 19 x 35 and is 100% mexican tiles, which are a nightmare when it comes to balancing furniture, and especially equipment. I tried similar adjustable spikes to the Daytons, and found them hard to place and adjust under speakers.


Consider that rooms are usually compromised in many ways, furniture, dimensions, type of walls (dry wall/stucco over lath...) so, my solution was to buy dollys from Harbor Freight, which have rubber wheels. @ ~ $25/set, an added bonus is the ease to move the speakers around to find the sweet spot

hth

@jmphotography ,
There seems to be two  schools of thought when it comes to isolating speakers.
One, like millercarbon aludes to uses springs to isolate speaker vibration.
(And, I do use the Townshend products under my equipment, though not under my speakers).
The other is one that Vandersteen uses, which entails using a thick piece of marble on which the speaker sits using spikes that are set on a special felt that reduces movement and anchors the speaker to the marble base.

Being a cheapskate, I opted for 3 inch butcherblock with some sorbothane pucks under them. It works well for me.
YMMV.
Bob

There are a couple of big benefits of outriggers:

- speakers are more stable and less likely to tip over from side forces.
- super easy leveling
- minimizes contact with flooring.

The other thing to keep in mind is to minimize the back and forth motion of the cabinets.  After you put the outriggers on you may want to try adding mass to the top of the cabinets.