Dave
I recenty asked Gaspar the same question. You have to arrow to the Tx on the bottom menu bar. Then you press right arrow 2 times and Mx appears. I then pressed down arrow and it then displays the normal Xicoy display. Once you have displayed it the Jeti box seems to retain it in the memory so you can switch between the usual parameters and the tx engine screen without having to do all the arrow presses. If you turn off it does not remember it.
This means you can use the Jeti box as an EDT but you cannot edit it just view it.
I am just getting to grips with the Jeti box amazing bit of kit. Reminder for all that you can use it with any Rx and send the telemetry signals via the supplied Jeti Rx. I use mine with 18SZ and an 14 channel Rx. I have a FC1 installed in the plane. On my first flight with it I found that the Rx regulator switch was not supplying sufficient voltage and the FC1 was tripping out. The Futaba Rx is amazing as it did not cause any problems with the widely fluctuating voltage but I guess it would have only been a matter of time.... the FC1/jeti certainly saved me a plane. Don't forget that both the Jeti box and the FC1 store data for later download.
John