How does MIT vary the impedance of their cables?

I have a pair of MIT 330's that are "medium" (47~100ohms) and I need "low" (10~47ohms).
I was wondering how MIT alters the impedance in their different versions? I'm guessing that it's with the use of a resistor in the network box? I thought that if I could open the box and jumper the resistor... Any opinions?
Peleon: There may be good reasons why they would pot the circuits, but I do know of one case where someone opened up a network box on a cable and found absolutely nothing but potting compound. The cable just ran right through it. (The box at the other end had a resistor of some sort in it, if memory serves.) So caveat emptor.
Speaking of MIT - I was deeply enthralled in a Clapton blues tune the other night and wham - left speaker goes dead. After some tinkering with everything, especially the speaker cable, I booted back up and it worked but the soundstage was pulling way right - the voice was dead center but drums and rythm were skewed to the right. When I twisted the network box everything centered up..must be a short or something screwed up in the box. Fortunately I have a pair of Kimber's for back up so I know it's definitely the cable. What the hell is that all about? Ever happen to anyone else?
I would drop MIT a line and ask them about the problem. I have corresponded with them on several occasions and have always gotten very informative replies. Good luck.