I posted in the ICOM forum, but no one could help (with the following problem), therefore I wanted to ask if somebody here has an idea.

I'm using a SDR created with GNUradio to transmit and receive GMSK signals in FM-D mode between an ICOM IC-7100 and IC-9100.
If the signal from the SDR is send to the IC-7100 as audio signal from the pc soundcard via an audio connection to DATA2 socket, the signal is correct transmitted to the IC-9100 and the input of the receiving SDR (connected via USB-cable to the IC-9100) is shown in following link.
Example for klinke audio connection
If the same signal is send to the IC-7100 via a USB cable to the USB-port to use the internal soundcard, the received signal at the IC-9100 is not correct.
Example for USB connection

I tried different settings (like 'USB MOD Level', '9600bps mode', 'DATA MOD' is set to 'USB' to use the input signal from USB-port, ...) to fix the USB connection problem, but no success.
I got comparable results while using the IC-9100 to send and the IC-7100 for receiving.
Does anyone has an idea what could be the problem with the USB-cable connection.
I tried it on ubuntu 16.04 and to be sure, installed the ICOM USB driver on a win 7 pc, which resulted in the same problem.

Thanks for your time and help.
Best regards