Was the original mic the one shaped like a hockey puck or the one shaped like the Eiffel Tower? Those two are not interchangeable, but the ACM1s generally are. Check the FAQ link I just posted.
To first clarify, I do not have the receiver & components yet. I'm thinking of purchasing a used model. To your question, the DTR 6.8 manual shows the "hockey puck", and some research shows that this model originally came with the "hockey puck" mic. The mic I have (the ACM1) is the "Eifel Tower" model.
I also (now) remember that my mic (ACM1) was during the "mislabeling" issue of Onkyo/Integra. So, I'm not 100% confident that it is an ACM1, it could be an ACM-1H.....
So, I'm thinking the Integra will require a completely different mic. Thanks for your quick reply!
The puck mic is definitely not interchangeable with the Eiffel Tower mic. One problem with the latter is that they have no markings on them - the only designation is on the box the mic comes with, which could have course been misplaced or swapped with another.
If buying used, I think it is essential to be sure that the mic accompanying the unit is the mic it was originally supplied with. Using an incompatible mic will give you unpredictable results. Personally, I would not buy a used unit that didn't come with its original mic for that reason. As you point out, you cannot even be sure, if you approach Onkyo to buy a new mic, that they themselves fully understand which mic you need. Audyssey may be more helpful to you in fact and an email to their CSR might help.
Bottom line is that the mic is a very important part of the Audyssey system. Good luck.