Suggest not including the DX8 on short list. The entire family (DX6, DX7, DX9 & DX18) have all been refreshed and feature a shared programming model as well as long list of new features. The current DX8 is the old generation at end of life.

Having said that, the current Spektrum telemetry model supports monitoring and logging of 1 temperature sensor, so you have to be OK monitoring the rear only. I have this issue with my twin as well.

Cheers