1) Upnp discovery can indeed be very slow, and some devices are better than others. In my experience MC is pretty good at discovery. Perhaps the Sony is initializing itself or downloading stuff ?? Or you firewall is blocking it ?? Try waiting a day or two, sometimes these issues just go away...
Well it shows up in Windows fairly quickly, it's just that Media Center seems to take its time.
For some reason it shows up as both a server and a zone that can be played to in Media Center, but the "server" often shows up a few minutes before the DLNA device does, even though they show up at pretty much the same time in Windows. (see the attached image)
2) The Upnp Seek function often depends on what type of media you are playing. What are you playing? Try setting MC server to convert to PCM rather than playing the original format.
Unfortunately I've already been converting to PCM for the Volume Leveling feature.
3) Synchronising the UI display when using two separate control points is notoriously bad in UPnp. It can be done but most vendors (including dare I say it JRiver) will tend to blame the other party. I suggest you ditch the Sony App and just use MC and Gizmo -- then at least if it doesn't work you know who to talk to 
When I use JRemote to control now/next/stop things seem to work correctly.
The reason I was using the Sony app is because it's the only way to access the speaker's built in DSP controls, and because you get nice large buttons that fill maybe 1/5 of the screen, instead of the tiny ones in JRemote that only appear when my iPad is in landscape orientation.
4) In Upnp v1 there is no multi player sync capability. It has been added in v3/4 but nobody has really implemented that yet.
Is there any way to know what version is being used? They are the new SRS-X7 speakers that were
just released here.
I thought Media Center was supposed to do its own synchronization for linked zones though.
I'm unsure about whether or not I'm going to keep the speakers (bought a pair of them) as this has been quite frustrating. I might post something about them in the speakers forum later.
I see now why people are willing to sacrifice high res support in favor of Sonos/AirPlay because those typically do what you expect of them.
If the linked zones start playing out of sync, try adjusting the zone link timing in the context menu for one of the linked zones. You can adjust the sync up to 2 seconds in either direction, so you can at least get them synced from the outset. Drift is harder to deal with, but making sure things start synced can help a lot.
Ah, I'll have to give that a shot. Very frustrating when I can simply play to Airfoil and everything just starts playing completely in sync without any drift. (that I've noticed)
I really love Media Center's library management features, but relying on "standards" like DLNA for networked audio seems to be very hit and miss, and it's quite disheartening.
