The D-LINK DSM 320 must work (is in the hardware compatible list from Nevo)
The Helios X3000 seems not to work ( [Link: twonkyvision.de] ).
For audio i use Soundbridges en SoundbridgeRadio. They work.

Problem is that l lot of the devices have support to read upnp servers but not have implemented (or bad) the upnp part to let them be controlled remote (like the Nevo SL will use if using the media zones).
Most users do not need it zo it is not on top of the list of futures to add.

I own a Ziova CS-505. It also can read upnp servers but can not be controlled using Media Zones from the Nevo SL. This is a known limitation of the Ziova. There are plans to include support for this in future Firmware upgrades (can't wait).

You can also try Cidero (PC software) to see if there is any UPnP controling possible.

Rob