Seeking recommendations about material, design, makers of low-lying rack for gear

That's what I would do, have some solid low profile stands made, for some of the gear anyway. Some like the mono amps might be better on Pods on the floor. Usually with transformers in the back the front is light and so a Pod under each rear corner plus one in front balances nicely. This can have the effect of the component appearing to float just above the floor.    

Also everybody likes to put things facing forward, when really they don't have to be. Like my sub amps, they are off to the left and facing outwards. They could also be at an angle. Turning things like this can make interconnects reach a lot better. This all falls under the heading of sounds vs looks. I can do woodworking but for now no time, and can only wish I had a guy able to make because I know what I want just no time to make it.

Are you saying that one long low rack is not a good way to go? I definitely am going front and center, but are you saying do two low racks?

I'm saying it is all trade offs, everywhere, all the time. Everyone has their own particular individual situation in terms of what they have now, what they plan on doing, how they want it to look, what they are willing to deal with in terms of convenience, and more. Like 30 years ago when I was, ahem, 30 years younger having my turntable on the floor, having to get down on the floor to do everything, it was no big deal. I ran my Basis on the floor for a year or more while I tested and figured things out. Now today it would be a total non-starter. I built my rack the height that it is for ergonomics as much as sound. Compromise. Trade off. Everywhere.   

Anything in the center, anything at all, it will reflect and this will degrade imaging. It is real easy to test this, as easy as buy one sheet of Owens Corning 703, cut it up and start moving it around. Not exactly the same as moving components but real close and a lot easier. I did all kinds of stuff like this way back when I was all young and spry and having to figure it all out because hardly any info out there back then.   

There's a very old photo from when my system was on a center rack. Even back then the imaging was so good I had a guy one time peek under the blanket, absolutely convinced there had to be a speaker behind it! https://www.theanalogdept.com/c_miller.htm  That blanket is a clue, you can ameliorate reflections with absorbers all kinds of different ways.  

That is why after trying a bunch of things I made my rack with round columns and a curved front and corners. No right angles. Not facing forwards anyway. Avoid racks with big square flat faces. But don't worry too much about how good the rack is at vibration control, because 90+% of that comes from Pods directly under each component. Or under the whole rack. Or both. These tend to take the rack out of the equation, except for the way it reflects sound. Use all that to creatively select one that suits you and your situation. That's the way I approach it.  

Like, one creative solution, two low racks left and right near the front wall. Components go on those. This leaves the most significant reflection zone in the center clear. Put your preamp on Pods on the floor, feeding amps on the floor on Pods. If the preamp is all remote control you hardly need to touch it anyway.    

But there are so many odd variables this might not work at all. Sometimes everything will reach with 1m, other times inputs and outputs are opposite ends too far apart. You just never know. That is why I give general info and hopefully enough you can figure it out from there.

I was thinking something like first off you could put the amps directly on Pods without even a short rack. But depending on what your standard is for looks you could spend a lot and have something that looks good but not be anywhere near the sound quality improvement of Pods. That is where the cheap rack with Pods comes from. I would use 3 per amp by the way not 4.  

I've used them directly under components and also under racks. Directly under a component is a bigger effect. So that is what I would do for the mono-blocks. Personally I would skip the rack altogether and put the amps right on the Pods. They go by the way directly under the chassis, not under the feet. This both helps keep a low profile and also works better because the Pods are in contact with the chassis not the feet. Also makes it easier to use 3 vs 4. Totally the way to go.  

Under a rack, I first put my turntable on Pods, then later got some of the really big ones to float the whole rack. This works great but is something to think about because it is after all equipment you handle. Speakers on Podiums only move when you touch them, which is not often. Racks however you touch that stuff all the time. The slightest touch and the whole rack moves. It is not anything to worry about, totally stable, but odd beyond words to see and so I mention it! My rack is so massive, at least 750 lbs, it sways crazy slow at about 1Hz. Maybe less. Anyway it definitely does work that way.    

Whether it is more cost-effective to do the whole rack or individual components, hard to say. What I can say for sure, putting them under a component is a lot easier than a whole rack! I would lean component for that reason alone.        

I was focused on the mono amps and would totally recommend 3 Pods under each, and skip the rack. But now I notice you also mentioned a low rack for components between the amps. This sounds a lot like what I have. The lower you keep things the better in terms of reflections. Also it is good to break things up by having them staggered in terms of distance. A wide flat rack is not so good in this regard. I actually played around with stuff like this a long time ago. Even fairly small stuff if it is flat it reflects enough to hear. Not big time, not very much at all in fact, but enough you can hear it. I had a guy over one time he noticed the imaging not as good on one side as the other, we figured out it was an LP leaned up for show. Moved it, better. One LP.    

Not big, not gonna kill you, but there. Moving everything off to the side comes at a cost as well. Wire quality is huge. We have only so much money. For sure you move your gear to one side you will be afraid to spend what it costs for wire, you will cut corners on that, and this will result in worse sound than if you left the gear in the middle bought the better wire and lived with the reflections. Take it to the bank. Put your stuff off to the side if you must for looks. But don't kid yourself that it sounds better. It won't.   

That said, looks matter. Not everyone wants the kind of mess I have, no matter how good it sounds. I am sick, and probably should be committed. But everyone knows that already.    

Honestly, Townshend Pods are so good I would focus above all on finding the rack with the looks you want, and rely on Pods for sound quality. Since nobody makes a rack that can compete with Pods on a price/sound quality basis, but plenty make racks that look real good for the money, this will also be the most cost-effective way to go.