Vertical Stacking Equipment

Hi rbschauman

I think there's nothing wrong with your initial approach of using the Nordost’s Sort Kones, as long as the Kones are capable of carrying the combined weight of the stack on top. E.g. in case your stacking all 4 components, the total weight will exceed 80 lbs, meaning the bottom ones need to support >80lbs, whereas the top one only 16-25lbs (depending what you put on top). I really like elliottbnewcombjr's suggestion to put glass shelving in between. Not sure whether that's possible in your cabinet though. If you think the Nordost Kones are too expensive, I used Stack Audio Auva isolators, those are very good: https://stackaudio.co.uk/product/auva-equipment-isolator/ Make sure you order the correct version depending on your weight requirements.

More affordable versions (not as sonically good as Auva's) would be the IsoAcoustics Iso-Puck Series Acoustic Isolators (Iso-Puck Mini, 6 lbs max/Unit, 8-Pack) https://www.amazon.com/dp/B07V25PWQL?th=1 These come in different weight classes.

Good luck!

@rjvissers +1  Yes, proper equipment stands are best, but you knew that already.  You are looking for less capital involvement.  Herbie's are also quite good.  Cumulative weight will be an issue risking cabinet deformation.  Good hunting.

You can space them apart, stacked, by using four  sorbothane pucks between them - try and avoid placing them to cover any ventilation slots.

@rbschauman no bueno!

1. your phono and line stage preamps have tubes. Stacking those is highly NOT recommended. You deprive these components of proper ventilation. This means heat will shorten the life of tubes and the overall lifespan of components. If you hsbe a microphonic tube, best of luck as it will pick up and send noise to your speakers. 
2. EMI emitted by each component will creep in and cause sound degradation 

3. Phono stage will pick up EMI and RFI from other components due to extremely high proximity. This will result in hum and may probably even hear other types of distortion.
4. Tuner will compound the issues above.
 

I will be shocked if your system, after having it setup the way you want, will perform properly.
Footers will do absolutely nothing except possibly leave scratches or other types of permanent marks on covers. 
 

If I were you I would find a way to spread the components out. 

From the manuals.

To maintain proper ventilation, mount the Premier 16LS horizontally on a flat, hard surface, and take care that the ventilation holes in the bottom are unobstructed. Allow at least two inches of clearance above the unit and keep the cabinet or shelf open at the back. Vertical installation is not recommended.  

The Premier Fifteen dissipates sufficient heat that it must be adequately ventilated. Mount the unit horizontally on a flat, hard surface, and take care that the ventilation holes in the bottom are unobstructed. Allow at least two inches of clearance above the unit and keep the cabinet or shelf open at the back. Vertical installation is not recommended. 

Because the DF2 cd player dissipates very little heat, ventilation is not an important consideration, allowing greater flexibility for custom or built-in installations. Of course, reasonable judgement must be exercised to see that the DF2 does not obstruct ventilation required by amplifiers or other equipment in the system. The DF2 is designed to be mounted horizontally.