The only incompatibility would occur with that amplifier relay and the buffer relay should take care of that just fine.
I also assume you are doing this tuning in the CW mode since that's the best way of doing it. If there's any reasonable output from the '718 getting to the amplifier you should be able to see the results on the amplifier's meters. I hope you got a manual for that amplifier, you will need it! Follow that manuals suggestions for tuning.
Since the amplifier seems to be working with the '101, I would think there's a problem in the connections with that buffer relay and the 718. No idea what that might be. OR, as was suggested, the inputs for that amplifier aren't even 'close' to being right.
Good luck.
- 'Doc