Sounds like a good theory to me.

Doesn't DPL (I) require some sort of built in encoding in the L/R signal the decoder is fed? If it doesn't get that encoding, wouldn't it just mess up the sound? I don't know; I've never used a DPL I receiver; I know that DPLII will take any source and "decode" it.

I am the Doctor, and THIS... is my SPOON!