Sorry to be so confusing.
DSM and DSM2 are different versions of Spektrum technology. Read the following post:
http://www.spektrumrc.com/DSM/Technology/DSM2.aspx
JR and Spektrum share the same technology, so a JR 2.4 Tx will work with a Spektrum 2.4 Rx. The opposited is also true.
The earlier Spektrum Tx and Rx used DSM. The later models use DSM2. It should be marked on the box that the Tx and Rx came in.
A DX5 is a DSM Tx and can only be used with a Spektrum Rx that is DSM. A DX7 uses DSM2 and can be used with any JR or Spektrum Rx.
You cannot use JR/Spektrum transmitters with any other manufacturers receivers.
You cannot use JR/Spektrum receivers with any other manufacturers transmitters.
The same is true for every other 2.4 Radio manufacturer such as Airtronics, Hitec, Futaba, etc.