Anyone ever opened MIT cables?

Iceraven: Why should I explain why? I didn't design the cable, and you can read it all at the MIT site. I tell you what, I will now. It's what you said, a form of LCR circuit that's in PARALLEL with the signal's path (i.e., across the positive-negative conductors)...Transparent Cable supposedly uses a series resistor, besides some form of LCR circuit, I gather. The ones I've heard from them do sound like something is in series, to me. Lots of things are going on with the design of MIT cables (and it IS patented, for what that's worth), and I'm not an electrical engineer (my brother is, though). I AM a speaker hobbyist, and know that a Zobel filter is used in parallel with woofers, to gently roll off their response BEFORE crossover. Now, as to WHY this works with cable, I can only assume the stated methodology at the MIT website, is somehow working (and that essentially all of the significant rolloff occurs untrasonically...but then, rolloff isn't the only thing the termination networks do, as you observe). I can also say that these won't work for all equipment, but when they DO work, it's better than ALL other cable types. ICERAVEN, YOU CAN DEMO THESE FROM TCC, OR JOE AT OVERTURE IN DELAWARE, AND LIKELY DOZENS OF OTHER PLACES. I recommend you try, if you have a solid state amplifier, or if you otherwise find your music lacks "weight", "slam", and "duration". If it doesn't lack these things, then you might not like what most MIT cables do in such a context.

The "boxes" are not filters per-se... The inductors, caps, R's in the networks are, to my understanding, a Group Delay Equalizer. This accomplishes the time-alignment of various frequencies traveling down the cable, such that they arrive at the speaker's terminals simultaneously. MIT explains that this phase-correction may contribute to perceived louder-sounding (and quieter = less noisy) performance than with a non-aligned cable operating at the same power level. I only have their 3rd, or 4th-best cable down from the top. Still kinda pricey, but so worthwhile! GREAT product. Spectral even 'requires' the use of MIT with their gear. Certainly a respected manufacturer, not to mention their design guru Keith Johnson. Think he just might know something?

My understanding is that they affect impedance, and therefore use a parallel filter network.

No once again they're expensive tone controls. Spectral is known to be bright at times why do you think they recomend you use MIT cables? And CARL if I remember right you have a krell amp another company that is know to be bright. So it's no wonder you like MIT. I had there 770 wire and 330 plus series 3 stuff. It still sounded great but I didn't need to "fix" anything when I got my new amp and I could now hear exactly how much the MIT wire was changing the sound compared to non boxed cable. MIT wire intentionally warmed the sound at the expense of some imaging and detail loss and a little less bass. That was unacceptable for me. I didn't need it to do that nor wanted MIT for that. So good riddens to $5000 worth of tone controls. However if that's what somebody wants and needs in their system and they are happy then more power to them. MIT doesn't suck if you need them but they are still just entirely over priced tone controls. And they still beat a lot of cables out there in the right systems that need them.

Most cables are overpriced IMO. They are also system and taste dependent. I use both Homegrown Super Silver and HT Truthlink IC's (switch them out). They sound entirely different and I like them both at certain times and for certain music. All cables (that I have tried) alter the sound and are therefore a type of tone control. Otherwise all quality cables would sound alike - which they don't.