I'm doing 1080 P MKV files containing H.264 at max without issue. No audio sync problems at all, and it's remuxing 5.1 audio to two channel stereo on the fly. Are you wired or wireless?
The kind of network should not be a factor in audio sync issues. I see this problem too on a wired connection. I guess you do not have this problem, because you let it transcode to stereo. dts-Tracks transcoded to AC3 5.1 show the audio out of sync.
I'm about to cancel also. My kids won't even use it because it freezes on them or you can't find the server. When I do come back on my shifts I struggle for hours until it magically starts working. Kids go right to the network. So much for making it easier for my kids. Glad they didn't offer a deal on the lifetime. I would have been one of the suckers. Keeps on freezes on every movie after about 1.5 hours. So @#$@ frustrating.