I have found that the X6100 is very sensitive to common mode current. Adding the amp will make it worse. As mentioned earlier, using a choke helps, and if you have enough coax in the line, 6 or 7 turns in a 7" diameter held together with cable ties will help. I have an EFHW and a DX Commander classic 1/4 wave 8 band vertical. No issues using the DXC, but the EFHW has common mode current heading back into the amp without chokes. My amp would lose control of the 6100 and flash that message, the swr between radio and amp would rise, and the 6100 would transmit 0w. Chokes help, but do not eliminate it entirely. Make sure the tuner in the 6100 is off. I will turn the amp tx power off, and transmit on nfm through the amp and check swr, and push the tune button on the amp if needed. Go back to the proper mode on the radio, enable power on the amp and good to go. It's extra steps, but it tends to keep everything happier. You have to remember that the X6100 is a computer made into a radio. It's front end is not as robust as a G90. It is not nearly as forgiving as a dedicated radio.
