One big benefit with Spektrum is that they ar compatible in both ways.
You Can use a DSMX receiver and Even the first AR6000 DSM to the older DX7 and DX6i.
You can also use the older DSM2 receivers to the new DX8 and DX6i X transmitters - (never tried to really old AR6000 with my DX8).
I was under the impression that the original DSM protocol will not work with DSM2/DSMX but I can tell you for sure that the DSM2 and DSMX work together. Each will automatically talk to each other and if DSMX is available they will always try to use DSMX but if either one only has DSM2 they will both use DSM2. This I have proven myself.
Agreed, spektrum rx/tx are either DSM2 or both DSM2/DSMX, i e backwards compatible. The protocol to use is established during bind and thereafter shown in the upper right corner on the "main page" of the tx. If both your tx/rx are DSMX-compatible and it still shows DSM2, you may want to look into what went wrong.