What exactly is critical listening? Who does it?

Critical listening is done in order to attempt to get the sound of your system to sound as good as possible to your ears. Once you're done with the room soundproofing and acoustic treatments, then come the equipment upgrades and only then you finalize it with subtle sound changes with various cables, fuses and isolation products. Each one of those changes will easily be noticeable and that's when critical listening is absolutely necessary. The hope is that eventually you never need any more critical listening. Audio nirvana. Am I there? No. Am I close? Definitely. It's a journey, just like the spiritual one.

@emergingsoul 

Thanks for your nice words. I got the Loki more out of curiosity than need. When hooked to my various digital sources, I quickly realized I hardly ever felt the need to use it as each has reached a quality of sound to my ears that really doesn't need equalizing. Except for some old poorly recorded CDs which I simply don't listen to anymore anyway. And for poorly mastered vinyl, I play them on my second TT hooked up to the Parks Audio Waxwing phono pre and the equalizing is plenty sufficient. In the end, I found the perfect use for the Loki, between my TV and blue ray player (all running through the main system), as it's lower sound quality can really benefit from the Loki. Now I can enjoy DVD concerts and you tube concerts without much of a drop in sound quality. And yes, diffusers in my room were badly needed. The ones at first reflection points made a huge leap in clarity and extending the soundstage.