How to properly put audio equipment on top of an antique buffet cabinet?

Just get a rectangular granite or marble slab. No need for the two MDF pieces. I have used this method myself!

Don't put a stone platform directly on that nice furniture. You would need some footers under the platform for two reasons; protect the finish and for isolation from vibration.
And the platform should be one piece, not two individual pieces.

A different way to gain isolation is...
http://www.symposiumusa.com/svelte.html

Isn't that a lot of weight with the components stacked?

I suggest a maple platform with cork/rubber pads under the platform.
https://www.ebay.com/sch/i.html?_from=R40&_trksid=m570.l1313&_nkw=cork+%26+rubber+pads&_sacat=0 I 

If you do use any kind of footers under whatever material you use for the base be aware that some of them, rubber, sorbothane, etc., will permanently stain a wood surface. Isolate any of those viscous substances from a wood finish.

Nice gear! Gorgeous antique buffet cabinet!
Now move that cabinet away from those speakers!!!
Ideally it would be on one of the side walls.
Do room treatment if you can.
You will be amazed how much better your expensive system will sound when it's set up correctly.
Jim Smith's book Get Better Sound is very helpful. It helped me.

Tom

If your goal is to protect that nice piece of furniture, you will not want any feet/footers/etc. resting directly on the wood. They may leave marks/spots on the furniture. You could get a granite/marble slab, or a maple butcher block slab and cut a piece of felt to put on the bottom of the slab. The felt should protect the wood finish from scratches or spots. Spray adhesive on the bottom of the slab will hold the felt in place.

I'd consider either marble/whatever, or even glass, which would show off the woodwork. As noted, felt or similar is probably the best to protect the wood.

G

1 piece of granite or marble or synthetic.
coner the bottom with felt furniture pads from home depot. All good. 

Chances are pretty good that the cabinet has a laquer finish on it as most older pieces have. No matter the type of platform you elect to go with as all suggestions will work fine you will need as large a felt 'foot' as you can fine, 1"-2" if you can find them. Do not use rubber feet as they will leave marks pretty quickly in the finish. Might I also suggest moving them slightly each month the size of the felt that you are going to use. Idealy you would want to continually move the 'point load' of the equipment and platform as even these felt feet can be pressed into the laquer finish and leave a mark over time.

If you use the cork/rubber feet just cut a square washer out of felt or thin cardboard, to place between the rubber & wood top. If you use the larger feet you would not need a platform, just put them under the component feet as the larger size will distribute the weight over the top of the furniture.

Cork is not a good idea since it retains moisture. If you use felt, make sure it's synthetic with no wool or fur in it.

I generally won't put a heavy unit on an antique regardless. Best to have something that you won't worry about scratching or marking.

" Cork is not a good idea since it retains moisture."
Nonsense, those cork/rubber pads (I linked above) are used in the HVAC industry with heating and A/C units for vibration control, cork floats and does not absorb moisture.

https://en.wikipedia.org/wiki/Cork_(material)

Personally, I would not recommend either marble or a granite stone slab.
Although marble would look good and is somewhat inexpensive it is a poor choice sonically. Marble would be a better choice, also look good, cost more but once again sonically weak.
I like the suggestions others have made and go with a 2" or 3" think piece of nicely finished maple supported off your beautiful antique buffet cabinet by a means that wn't damage the wood.

How to properly put audio equipment on top of an antique buffet cabinet?

You have an NAD M2 that still works? Nice!

Your beautiful  17th century style 1920’s built sideboard is a big heavy slab by itself. I see anything other than simple sorbathane or rubber feet taking away too much of the visual and providing no sonic benefit. Do not use felt as it is the old finishes that over time will absorb the texture and leave a mark.

Possibly Herbie's Tenderfeet. They are neither sorbathane or rubber.
http://herbiesaudiolab.net/compfeet.htm

And to the OP; please pull your speakers forward to improve imaging.

+1 for Herbie's Tenderfeet, I use them in my system.

Thanks heaps for all the valuable feedback - amazing!

@roberjerman - I was considering a marble slab as replacement
@lowrider57 - I didn't consider the finish of the furniture :s Thx for pointing that out. Following your advice, I looked at the Svelte. One of the reasons I want something under my components, is that the cabinet doesn't have a massive top. It's with inlay and it's not that strong. The outer border is massive 4 cm (cherry?) wood. So a lot of pressure would come just in the middle of the Svelte, with nothing underneath. The components stacked are about 30kg / 66 pounds. With a marble slab underneath, it'll come close to 60kg / 130 pounds.
I'll take a look at the Tenderfeet, looks ok!
@dill - thx for the tip, these maple slabs seem to come in massive sizes only and I guess it'll look weird to have light wood on top of a dark wooden cabinet. No? 
The cabinet is not even on top, only the border is massive, in between is thin inlay wood, it's more decorative that way but anything that weighs anything can't stand there.
@sfar - hmmm is there any material that wouldn't leave a stain? There are some on the cabinet already due to it being used. I once placed volcanic stone on a locker. A year later, the wood was heavily damaged due to sulphur... so I'm cautious :)
@tomcarr - it's quite far away from the wall at the moment, I need to crawl behind it from time to time. Thx for the tip about the book, as you can see it's just in my living room with playing kids around, so limited options at the moment.
@reubent - The current "solution" has felt patches to stick underneath furniture underneath. Works like a charm!
@itjustme - would glass be able to carry the weight?
@stevea11757 - thx for the advice!
@twochannelami - you're a man of culture! I think that's rather spot on with regards to style etc ;) The problem is there is no massive heavy slab on top, only the border is massive. So I have to "bridge" the cabinet in order to put something heavy on top.

OK, so the construction of the cabinet changes things. You could use one large MDF base if you use the Herbies under the components. Even though MDF is not great material for sonics, the Herbies would absorb vibration and and the MDF would not influence the sound.

Or use finished bamboo as the platform. It is dense and when used under components it provides neutral sonics. Use Google to find the right size of bamboo.
BTW, using glass as a platform does not produce neutral sonics.

Buy a good wood cutting board from IKEA or Bed Bath & Beyond with felt underneath

Thanks heaps again.

• http://www.koenentine.be/documents/IMG_1348.jpg
  
• http://www.koenentine.be/documents/IMG_1349.jpg
  

Based on your feedback, I obtained 

• GAIA II feet to decouple speakers from the floor
• 8cm (3.14") thick solid oak blocks for the speakers, with the Gaia underneath
• Herbie's Fat Dots 
• 4cm (1.57") thick solid oak block for the components, with the Fat Dots underneath

Looks good, sounds good. Now I want to run Luc Arbogast's version from the Game Of Thrones title theme through it to hear the difference... but not when the kids are asleep :)

Looking very good!
Glade it all worked out ;-)

The only reason to put anything underneath the electronics would be to protect the nice buffet. Sonically there is no need at all.