Softphone connection ever stablished but no audio signal

Hello community,

I'm trying to get my Softphone running under Parallels 12 / Windows 8.1 on an iMac. The connection is established but there is no audio signal on my Headset (system sounds, youtube etc. no problem). I don't head the partner and he is not able to hear me. I am using a Jabra USB Headset. Already read that connection to Win machine and Mac / network mode can make a difference, tried both.

Any suggestions?

Thanks in advance...