Resolution: sent the 6300 to flex. They installed ECO 75-1006 at no charge. Now the audio sounds much better with the 500 Hz eq setting at + 1 db, the 1k equalizer setting is only +4db ,(rather than +10db), the 2k slider is at +6 db, 4k at +5 db. Overall tx audio now sounds like me face to face. However , they declined to run the audio to RF test I requested. I will run that later as time permits.