4 - Insists FrontPanel<->Coax<->ActiveSpeakers is good (assumes, natch)
3. Cable IS good. Front panel I don't know, but I assume it is.
4. This I didn't say. You are speculating. There are several things that could be wrong on this connection. Sound card, front panel, active speakers' DAC, active speakers' amplifier. Basically everything EXCEPT the cable. What on earth could be wrong with the cable ? The only things required for a cable are to make good contact (it does), to have a good consistency throughout all it's length (no reason to suspect) and to be able to withstand the amount of current/data transferred (oh yeah, good, thick cable).
4. I dare you get a brand spanky new one, stomp on it, or twist it a couple of times. This type of thing is exactly what causes a SHORT (there's that word again) between internal wiring. Remember the example I gave about 4-hour time waste? Simple continuity check on one end ONLY to see if there is FULL OPEN (a new word for you). Wires CAN go bad INSIDE the "heavy duty" (I thought I clearly pointed that out to you). Speculation - NO, A DISTINCT POSSIBILITY.
loudspeaker constructionNope, just CAN'T fail, right? We've had to disconnect a single "dump" (bottoms/subwoofer) box before a gig, leaving one double-15" on one side as opposed to two due to "rattling"/"buzzing"/etc to get through the gig to prevent being FIRED/BLACKBALLED (remember?).
To summarize -
1 - Cable<->Front COULD be bad (untested ASSUMED good)
2 - Coax<->Speaker COULD be bad (untested ASSUMED good)
3 - Coax<->SpeakerConnector (on the Speaker) SHORT (untested BACK OF SPEAKER)
4 - Speaker Partially Blown (coil rubbing - untested ASSUMED good)
5 - Speaker Amplifier Failing (untested ASSUMED good - see #3)
---- (also note that same problem of Card Dirty/Failing is same as Speaker Amp)
6 - Speaker CircuitSwitchBetween(INTERNAL inside Speaker) failing/shorting between Analog/Coax
7 - Speaker Crossovers (internal) FAILING
See all of those ASSUMPTIONS? Big Fail, in my book...
Seems to revolve around the FrontPanel/Coax/SpeakerFailure. My money (ASSUMING #1 #2 is good, as YOU assume) is on some Speaker Component failure (see #3->#7). You sure have a lot of faith in those Active (nearly unheard of Brand) Speakers, don't you? At the price they charged, I would suggest replacing them with Name Brand (e.g. Bose).
Funny how the OTHER
Output -> POWERED-receiver->UNPOWERED-speaker
works just fine...
One more troubleshooting tip - raise the Gain until you hear that "whatever" and listen CLOSELY to each of Low/Mid/High. Whichever one is "whatever", it's just THAT part of the Speaker that's failing OR the Crossover Burned Out and is allowing Low->Mid and/or Low/Mid->High, thus allowing a Frequency through not meant to be there. Crack open the Boxes and disconnect THAT Speaker inside and see if it STILL "whatever". (Didn't research Crossovers either, did you?)
(Yes, Speakers-aka-Drivers can be replaced with equivalent or slightly higher powered @ same Ohms.)
BTW, I believe I stated you DO have "Pro" equipment - correction: Semi-Pro. Sennheiser, BTW, is top-of-the-line and not too cheap. You provide a Name Brand Sound Equipment (any kind) and I've probably used it.
Might want to LOCK this topic as it's becoming an exercise in futility...