I had the same problem with my setup. No issue playing music on the computer from firefly on the NSLU2, but as soon as I tried playing on my Soundbridge M1001 I would be lucky to get one song before it lost the Firefly server.
I´m off to check my logs now to see what´s in there. However, I do seem to have solved the problem by changing the database type from ´sqlite´ to ´sqlite3´ and rescanning the collection. Don´t know why this should make a difference but I haven´t need to reboot firefly for a day now and have had no problems listening to streams on the Soundbridge.