Need Help!

I use IsoAcoustics and like them, but don't have a turntable myself:
https://isoacoustics.com/

Okay so here's your custom rack solution: 3 feet of 4" ABS, one bag of construction sand, and one butcher block cutting board. 

Before you balk at the ABS take a look and see how good it can look: 
https://systems.audiogon.com/systems/8367 Mine's gotten kind of hazy after 15+ years and I'm too lazy to oil it but those black round legs are all ABS and the bottom ones still look awfully good even after almost 20 years. 

The trick is to first remove the crap lettering and marks with a solvent like paint thinner, then sand and polish. Buy the ABS and cutting board some place like Home Depot and have them cut to size. 8" to 9" long will give you plenty of air space. Fill with sand, cap the ends off however you like, lay the cutting board across them. Do it right and it will be an improvement. Doing it right means mostly experimenting with what goes between the cutting board and the legs and the turntable feet and the cutting board. 

For even better, cut an additional four 1" tall sections of ABS, fill with sand, and use as footers under the turntable. 

Couple ideas:
https://www.audioadvisor.com/prodinfo.asp?number=PGVUXAS

https://www.homedepot.com/p/Noble-House-Bartlet-39-37-Clear-TV-Stand-Fits-39-in-TV-7628/307889422
Put the turntable on top and the amp underneath, for the homedepot one, just simply remove the middle shelf.

If butcher block doesn't cut it for you..
Visit a local stone countertop company.  They Always have 'drops' from cut-outs for sinks, that end up in a pile, or 'end drops' since they generally have to buy a full sheet to process.
Have 'em cut it to size, clean up the edges, and viola'!
You're stoned....or a syth material for a 'modern mood'.

I've some dark marble shelves recycled, supported with 4x6's with routed edges.  'Stable' is an understatement...;)  Takes 2 to move it empty.

Good luck, have fun.
J

There are wall mount TT racks. They’re great to isolate vibrations coming up from floor standing racks.

https://www.turntablelab.com/products/rega-wall-mount-for-rega-turntables-black?variant=864190044581...

Don’t overlook man-made composite counter top materials. Quartz and Corian are very dense and have good resonance characteristics. Corian is my favourite because it can easily be cut and machined with woodworking tools. You can even make a layered Corian top with the middle cut out and filled with construction sand for a very nice look and even better resonance characteristics. 

I want to thank everyone for your very thoughtful suggestions.  However, I should have pointed out the problem I am experiencing is not from vibration(s), per se, but, rather, from acoustic feedback picked up by the TT cartridge at high spls.  At least, this is what an audiophile tech told me after I explained the issue in detail  The TT cartridge is so sensitive that I get a hum in the speakers at anything over a 50% gain, or so, on the MAC.  Loud, I know, but sometimes I just like to play things loud.  If this is, in fact, the issue then the only solution is to get the TT as far away from my speakers, as possible.  So, imhififan, I'm inclined to think your suggestion of the Pangea amp stand just may be the solution.  I hope so.  Otherwise, I'll have to consider much more drastic steps (i.e. high-end TT interconnects or re-arranging the entire living/listening room).  Thanks, again, all!

You might benefit from properly shielded interconnects from the turntable to your phono stage. The old way of using the signal return path (signal “ground”) is completely ineffective at blocking EMI and RFI noise. 

You should have at least 7 " of space in between shelves. You can place the amp on either the middle or bottom shelf. Place footers(I suggest cost effective Isoblocks) under the amp 1" in from the edge/ back of the shelf and let the 4.5" (20%) of the amp canterliver over the edge. There is enough weight - (the transformers are in the front of the unit, heaviest part) in the 17.5" (80%) of the unit that is directly supported by the shelf to keep it stable. I reccomend the bottom shelf to get the most separation.

Additionally I would bring your speakers forward toward your listening postion to get even more separation and better overall sonic presentaion. I also agree with those who suggest taking abother look at your cabling and investing in an upgrade if neccessary.

https://shop.mapleshadestore.com/Mapleshade-Isoblock-Sets_p_1224.html

In general I don’t think glass is a good option for shelveing, here is another option to check out if you are looking to invest in a isolation solution.

https://audiophilevibrationcontrol.com/

Best Of Luck

This is offered just in case anyone happens upon this thread looking for similar solutions.

After several email exchanges with MAC Labs, Mofi, TT lab and others, I eventually solved this problem without spending any dough.  I got rid of my AT&T DirecTV service, not because of this but because every since AT&T took over DirecTV, service just sucked out loud!  Almost $180.00 a month and the worst service I've ever received from any enterprise in my life!  One tech told me the DirecTV receivers I had just below the amp but a good distance away from the TT and the ethernet connection for these things might be causing the problem.  I still have the ethernet connected to my NetGear WIFI router.  So, seems like this was the funky DirecTV receivers.  That, or another suggestion I employed, as well.  I made certain the amp, TT and power conditioner power cables where separated from each other as much as possible.  Lastly, I upgraded my speakers from my 20 year old trusty and thoroughly wonderful Paradigm Monitor 9 to new Revel Performa 3 F206.  Could be these are better shielded?  Don't know but the TT rumble is now history and the music rocks.  However, I am not stopping there because all of the techs I communicated with said I really should put more space between the amp and the TT, or more importantly, its cartridge.  I've got a new Salamander rack on order.

Thanks again for all the gray cell grist.  You folks are all truly wonderful!  Stay Safe!  Stay Healthy!  And get vaccinated!