You don't have to have multiple soundcards in order for zones to be useful. One of the great features of zones is that each one can have it's own parameters.
You can setup multiple zones using a single soundcard, each with it's own playback settings that are appropriate for different listening situations. Then it's easy to switch between them using the Zone Manager, rather than going into the playback settings fiddling with different settings. For example, I have one zone that is just normal gapless playback with Replay Gain enabled (for playing back whole albums or DJ mixes). I have another zone that is gapless with no Replay Gain (for certain albums that don't sound right with RG). I have another that is 2 second crossfade (for playing back random mixes of tracks), etc. I do have two soundcards, but I think I have about six zones setup for each of them.
Once you start playing around with zones, you'll probably come up with some ideas of how you can use them.
Rob