No expense was spared in the design and construction of the Phono Blocks. The Phono Blocks are at the pinnacle of phono preamp performance. It just doesn't get any better.
The 20/20 was designed to get the most performance possible at its predetermined price point. To get there, extra was spent to get premium parts and circuitry into the signal path. Consequently, some expenses were squeezed out of less important areas. Those trade-offs have worked very well. The 20/20 has delivered an extremely high level of performance at a reasonable price. It is an incredible performance value.
What if all the price constraints in the 20/20 were lifted? The price goes up, the performance goes up. It starts looking a lot like the Phono Blocks.
The actual signal path of the 20/20 is quite good. It uses a circuit very similar to the Phono Blocks. In critical positions, it also uses the same premium quality (and high cost) components. Very little was held back in that area.
The opportunity for upgrade is focused on a more refined power supply, improved circuit board properties and dual chassis construction.