Kling,
Just to clarify your situation, when you say that you tested with our test codecs, was that from your station Commander or the remote iMix? Also, have tried connecting to our test codec, from your station, with the iMix, using the line normally used by your Commander?
The other thing that that may be relevant is the age of your station Commander. If it has an old POTS module, you may find our new module could improve things for you. Contact our office in Indianapolis, they will be able to advise you on how to identify the module that you have.