[Gopher]

I can confirm there is a plug in there that fits the duet...

Would this do? 

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=120-537

Thank you for the confirmation.  It was ordered and recieved today!  Its way too early to say very much about how the sound changed and I only really lived with the SB Duet for a couple days in the first instance. But I do have to say that from the analog outs bass seems a lot more solid!