Those black boxes degrade sound?

They are not fixing anything other than phase differences introduced by the cables themsleves - that's how the manufacturer decides how much adjusting to put into the boxes. At least that's what the marketing hype says. I have heard legend that the cables sound better if you cut the boxes off, but I don't know who has actually had the chutzpah to cut up a set of very expensive cables for this purpose. Elizabeth - are you saying that you actually heard this done, with an identical pair of cables? What cables were they?
I do know that systems I have heard with MIT cables sound anything but smeared.

I do not think they wear out and actually found quite the opposite. My old 850 Reference speaker cables and 350 Reference ic's seemed to sound better over the years and were stellar right up until recently when I replaced them.

Regarding the comments about rolled off freq and smeared sound, I would be very curious to know which cable exactly, and with what gear because that is so very opposite of my experience. I have yet to find a cable that comes close to the clarity, accuracy, dynamics and overall "you are there" experience than MIT. They transformed my system way beyond my expectations and each cable has been more like a component change than a cable change. I can appreciate some may not be willing to make that type of investment in cable components but I cannot understand denying their efficacy.

NO, the ones I heard were handmade to sell on the market. I will NOT name them as the 'manufacturer' HAS attempted to sue me for insulting his trash. He is insane of course, as I have every right to post a review.. but the hassle is more than I need. So, no names. (Think small.. very, very small, AND crazy as hell.)
They are no longer in production, thank goodness.

as per usual, spouting off again about nothing which BTW "I have not heard"

tell us all, dear voodoo, how good that group delay sounds compared to your smearing reference standard

I have many years of experience with MIT and they are anything but smeared. They are actually the most grain free cables I have used - they might not be for everybody, but I have found in every system I have used/heard the one characteristic that is consistent is clarity and grain free sound.