I am actually a well respected member of the Supra community at www.mkiv.com
. I am also familiar with the ST185, and have a few friends in that community as well.
Calling a Roots blower "not a compressor" is semantics. It is a compressor or it could not build pressure. It just happens to be the least efficient of all compressors at about 60% (with new rotor seals). If you feed it pressurized air, it will put out more air than it would at atmospheric, just like any other good compressor. I completely agree it is the least desireable of all the supercharger types available. I'd take a Lysholm or Whipple over a Roots in a second.
Insane boost is a relative term. It's hard to find insane on a 2JZ, however, the 2AZ is not cut of the same cloth. It won't matter much how you pressurize the air with a 2AZ, the block just isn't up to much boost without major modification. Here is where I take strong exception to your statement "it all comes down to tuning". The block will not support high boost without major mods. Why are there no 1000 hp NSX's? Their blocks don't support boost without cracking very shortly after they are boosted. The tC will suffer the same fate. I'd be surprised if the stock unmodified block will tolerate even 8 psi for any significant length of time before it cracks.
AFA compound boost, twincharging isn't compound boost (semantics again). Compound boost is putting multiple compressors in series. Twincharging is using one method at low rpm, and another at high rpm to make a small engine perform like a big one (for the most part: BSFC says little engines with forced induction still need more fuel to make the same power). I understand the concept just fine, and I followed Toysport's MR2 Twincharging project many years ago. I have also seen one in the flesh at a shop near my house. They go really well with good fuel in them.
In any case, they make power down low with the supercharger and switch over to the turbocharger once the combination of rpm and load supports the turbo moving more air than the supercharger can move efficiently. The turbocharger is also inherently more efficient than any supercharger (except a Vortech, because a Vortech is just a gear driver turbo compressor section). I understand all this just fine.