I also have the model with built-in attenuator board and I control my transverter via the acc socket. On the KX 2 you can control the swr to the input of the transverter.
In the transverter mode of the kx 2, I increased the power from below so much that I am at 8 watts output and thus get a clean signal.
At the moment my transverter is on the table and I’m about to install the tcxo as Chris did:
So far it has given me a lot of joy. But it is a pity that there is so little going on ssb.