If you can tell the difference from the time after you've unhooked the player, sent it to him, he's modded it, sent it back, and you get it hooked back up, then there was something seriously wrong with the player, or you've fooled yourself into believing there was a change.
The only way to judge these "improvements" is to be able to blindly switch between a modded and unmodded player moment to moment. I still have my doubts if anything could be heard. Perhaps measured on very fine equipment, but the effect of the room will so far outweigh any electronic upgrades in well designed gear that it makes the pursuit futile. Heck temperature/pressure variations from weather will have a bigger impact on sound than these mods.
