The problem here is probably the dsm-520. This device must support the remote rendering command (UpNp command). If it does not It won't work. Although UpNp is a universal protocol, a company which develops a UpNp device is not always implementing all the commands. I would suggest to report this to dsm and then they might (hopefully) implement this in the new firmware.
One question, have you tried cidero ([Link: cidero.com]
)? If that works the problem lays with the 9800i