Crutchfield doesn't know the answer, so I figured I'd come here and ask some smart people....
I've got the clarion M309 headunit in my boat. It has a CE-Net port on the back. I would like to add a sirius tuner, and clarion's older models, the SIR-CL1, can be had for around $50. It also connects via CE-Net.
However, the M309 manual doesn't say whether the deck is backwards compatible with clarion's older sirius tuners, and only suggests connecting the current model tuner. The current model tuner is over $100, and I don't want to spend that much.
So does anyone know whether the old CE-Net sirius tuners are still compatible with the newer clarion headunits?