Hi:
I was the beta tester for that setup, and I have the same headset. For some unknown reason the automatic setup procedure on the Jabra base station doesn't work. If you instead use the manual procedure, and select the first choice for "clear dial tone" (A), then it'll work. You can adjust the headset's transmit volume by starting with the middle setting (5) and then calling a patient friend, talk to him/her, and tweak the transmit (mic) volume up and down.
Just a reminder of the standard "newbie" error: use the OBiTALK web portal in "Expert" mode to make these changes, not the phone's local web page. The portal will overwrite the settings made on the local web page. To change a parameter from default, you need to remove the check marks from both check boxes to the right of the parameter. I've attached the settings that work well for me. I have a slight hearing loss, so it might be a bit too loud for you.