I came from the original xformers and had both the Vocm and nickel xformers installed. It is by a wide margin the biggest jump in sound quality of any electronics piece of gear I have purchased in my audio chain.... ever. I do recall reading on the PS Audio forum of folks who had gone from the Encore 4400 to the nickel xformers and they reported a significant increase in performance. Based on the design of the DS using the xformers as a low pass filter, my educated guess is the nickel xformers will provide the most significant improvment compared to Vocm mod.
WRT disappearing threads from the PS Audio forum. Huge props to PS Audio for hosting a forum that has a discussion of modding their products with input from the chief engineer. Interesting that you can discuss the mods, but they draw the line at describing what those mods sound like. I can understand that their focus is on selling their product and keeping interest in it. IMO, PS Audio could best serve their DS MK2 customers, by changing to a nickel core xformers in their MK2 and offer an upgrade path for those who have already purchased. IMO a used DS with this mod is likely the DAC performance to dollar king.