I am not sure if I can post this here, but here is how I am synching mutliple sound cards and only using one winamp instance for low cpu usage:
Pick up the KX drivers from http://kxproject.lugosoft.com and follow the directions at this tips and tricks post:
http://www.xlobby.com/forum/viewtopic.php?t=4704
Then find the out_ds.dll plugin and copy it and create new plugin such as out_ds2.dll. This will allow you to have as many directsound outputs as you need in winamp.
Set each different Directsound output to handle a different output from your sound card (I use 0/1 on both of my Creative cards and the output from my onboard sound and so I need 3 direct sound plugins in winamp).
Then get this plugin at winamp.com:
http://www.winamp.com/plugins/details.php?id=147344
This will allow you to use all of our directsound plugins at once. Then when you play a song in xlobby you just have to select that winamp zone (I have mine called All) and it will play to every output you have. I have all 5 sets of speakers outputting using that one winamp instance (I am only using the very basic winamp lite for as little memory usage as possible).
I hope to add screen shots at a later date.