OR the outs, i.e. - speaker wires. As my speakers are powered by speaker outs and not pre-outs I measure them. Receiver could even have no any pre-outs, but in my case it is simply more convenient to access the speaker wires than pre-outs. If you think there is a difference - argument it.
There is no difference at all between the signal at the preouts and the signal at the speaker terminal, other than level. If you are connecting the speaker terminals to your soundcard I am amazed (and impressed) that you haven't fried it. Soundcards are not designed to accept these high level inputs. If I were you I would follow AustinJerry's advice and start using the preouts - there's no difference at all and you won’t be out buying a new soundcard next week!
You are right that the speakers are powered by the speaker outs, but the signal the speaker outs receives is identical to the signal the preouts put out, except at a much higher level. If you want to measure the result of MultEQ filtration in the room (at the MLP), then again you need to follow Jerry's advice and use the mic in the room to measure the acoustic output of the speakers in the room.
You seem to be conflating two different things. Measuring at the preouts will show you the MultEQ filter that Audyssey is creating in order to correct whatever problems Audyssey has detected with the room. To measure the effect of that filter (or filters) you need to measure the actual acoustic output in the room itself, with the mic at the listening position.
To determine if the mic is faulty or not, you will ideally need a known good mic to use as a reference. Connect the mic and, with Audyssey turned OFF, measure a sweep from it, using the preout terminals. Then put the suspect mic in the exact same position and, with Audyssey turned off, measure a sweep from it, using the preouts. Then compare the results. If the suspect mic graph differs significantly from the graph of the reference mic, then there is likely a problem with the suspect mic. The graph will reveal that problem. For example, if the suspect mic graph shows a substantial roll-off at the upper end of the FR (compared with the known good mic), then Audyssey will try to correct for that and it will boost the treble and cause the system to sound overly bright or harsh. You can do this without a reference mic and if there is a really obvious problem (like a massive HDF roll-off) you can probably come to a reasonable conclusion that the mic is faulty, but if you have access to a known good mic, your result will be much more certain.
Edited by kbarnes701 - 12/9/12 at 3:28am