MDF Rack dampening question

I would start with filling the tubes with lead shot. Then if you add spikes make sure you use cone rest between spike and floor. I think butcher block would be a waste.
How thick are MDF shelves and are you sure they are MDF and not particle board? MDF really should deaden vibration which is why speaker manufactures love the stuff.
I think these measures would be a good start and possibly the solution.

I've got a Billy Baggs rack of similar construction and I find thick maple platforms contribute very positively to better sound. Not all components respond equally well to sitting on maple, but that's true of every audio proposition. MDF is a dull sounding poor excuse for shelving IMO. Manufacturers use it because it's cheap and performs reasonably well, pure and simple. Better sounding shelving and speaker construction panels cost a lot more than mdf. I also find Golden Sound ceramic cones between gear and mdf shelving are a good thing. I'm sure there are many other good choices. You just have to find what sort of sound you like. Galen Carol Audio's website has a good summary of the sound characteristics of various footers & cones which I've found accurate. If you want to spend more, Neuance, Gingko, and others make good isolation platforms. Basically, the money you save on a less expensive rack with MDF shelving forces you to spend more money to correct the crummy sound of MDF. Think carefully about filing the rack with lead shot or putting spikes on it if you ever want to move it to change equipment, clean, etc. Your idea to use damping material on the bottom of the shelving will help to ameliorate vibration, but it will still sound dull and lifeless.

Actually, MDF can work well when used properly, but its use in lesser designs has given it a bad name. What you should be careful of is mixing different design philosophies in regard to vibration control. Basically, you can either attempt to drain vibration as directly as possible or attempt to damp it at each stage. I prefer the first but I have used the other successfully. But a combination of the two is seldom successful. It also depends on the components you are using. Suspended sub chassis tables like dampened platforms much better than rigid tables. I have noticed this with VPI. The new tables have different requirements than the older ones. I would consider Kitty litter if you wanted to fill the tubes , I prefer it to lead or sand, Use of good cones under the shelf system or the individual units will help. You can combine this with use of maple blocks, Timbernation and Michigan Maple Block are good sources. Controlling vibration is a very critical element of good sound and there are several approaches , just keep track of what you expect each element to do.

The MDF itself is on the verge of providing to much damping,all that saw dust and glue. I once had a Michael Green stand which came with steel all thread rods that made the shelfs adjustable. Replacing the steel with brass made for a dramatic improvement in stage and dynamics,the rods where grounded/coupled with Audipoints. As Stan suggested I would not shut your system down with the use of sand or lead shot. Steel or brass bearings would be much better but costly. The kitty litter maybe the best value. I would fill the tubes only 1/3 at a time and then listen to the same familar recording at the same volume level, adding more each time until you hear the stage dynamics begin to shut down...and then stop. You may not get to fill the rods to the top. You will hear a difference with each additional pour. Tom

I filled the vertical tubular columns with sand. They used to ding like a bell when tapped, now it's a thud.

The shelves are relatively thin, and transmit vibrations easily. I'm going to try some dampening sheets under each (Dynamat Extreme)

How can I tell if the shelves are MDF or particle board? They're completely painted smooth flat black. How does that make a difference in my strategy?

I see many put their equipment on top of butcher block or other thick wood platforms with some isolators (cones, etc.)

Thanks!