I have a similar problem. Since the OP hasn't responded, I'm going to add to this thread to try and keep this in one convenient location for everyone.
I've had problems with multizone playback for quite awhile. I think I first tried this feature with MC15, but gave up because I could never get it to work. I assumed that one of the PCs just didn't have the processing power and memory to handle this. I've since upgraded to MC17 and I've also replaced the slow PC with a new more robust system. Here are the details:
I have a bunch of PCs connected to a home network. My routers and switches are all gigabit and the performance is pretty good. Streaming audio or video from one PC to another works fine, even ripped Blu-rays with 1080p and 7.1 DTS-HD audio. Also connected to the network is an unRaid server where all my media is stored. Several of the PCs on my network are running MC17, but I am just dealing with two of the PCs for linking zones. I will refer to them as PC1 and PC2.
I am trying to synchronously play music in multiple locations in my home using the linked zone feature. PC1 is connected to an amp that plays music in my living room. PC2 is connected to an amp that plays music in our family room, which is located in our basement.
Both PCs are running Windows 7 64-bit and have fairly fast modern Intel CPUs (i5s) and 4 GBs of RAM. Each of these PCs use the unRaid media server for storing content (all the audio, video, photos, etc. that are stored on the server are shared by all the PCs connected to our home network). Both of these PCs are running the same version of MC17 - 17.0.182. They both have 'Use Media Network to share this library and enable DLNA' enabled. Both are set to display cover art in the 'Playing Now' view.
I'm using PC1 to initiate the zone linking and I am not sure if it makes any difference which PC is used. On PC1, I select an album and pick PLAY. Then I choose the Player from the 'Playing Now' list and drag it over the PC2 Player. MC17 immediately creates the link and starts playing the song in PC1's playlist. The song is playing in sync on both PCs. This is great. However, this was after stumbling around with different combinations. During one attempt, I got a message box asking me to identify the "Master" and I chose the PC1 player. It worked for the first song, but then it stopped playing the rest of the songs in the playlist. This usually happened when I tried to initiate the link from PC2. I would try to play PC1's playlist on PC2 and after the first song, it would continue playing on PC2, but stop playing on PC1. Other times, it would just keep repeating the first song.
Playing a playlist from PC1 and initiating the link from PC1 works. On PC2's screen, only the currently playing and the next song are listed in the 'Playing Now' view. The link info between these PCs is only shown on PC1. There isn't any indication on PC2 that the two PCs are linked.
The transitions to the next song are pretty glitchy. This is probably similar to the OP's buffering issue, but not nearly as bad. When it transitions from one track to the next, I hear a little audio snippet of the next song and then some silence. After several seconds the next song started playing. I assume this is probably a syncing issue. I also noticed that the cover art in the 'Playing Now' view of PC1 disappears and is briefly replaced by the 'Play Doctor' screen during the silent delay between tracks. The next song starts playing in both zones and PC2 again only shows 2 tracks in the 'Playing Now' list - the current and next songs.
Does this seem about right, does everyone have audio glitches between tracks with this feature?
Is there something I can do to get this to work better when linking from either computer?