Yes, I have optical out that I run into a rockboxed Iriver.
Well, I made that adapter myself. I used a 7pin connector and put a optical jack inside. I would be making more of these adapters but it's impossible to buy 7pin connectors(they are discontinued). I've been hacking the 7pins off broken cables and using them. Since it's hard to find the connectors it is just easier to put the optical jack right on the sbm1. I have never had any problems with the optical cutting out or not working right. I get back to you when I have the parts ordered for the mod. I plan on only charging $35 shipped for the mod. Let me know what you think or if you have any other questions.
-Trenton