can i *separately* control the volume on each of these outputs?
You can control the volume of each of these outputs serperately. You will set up three seperate instances of winamp. Each winamp will need to be configured for a specific output defined by the kxdrivers. In xlobby, you will create three seperate audio zones, each zone directed at one instance of winamp. When controlling that zone, you will be able to control the volume seperately from all the other zones.
For further info on the kxdrivers, please view my post here:
http://www.xlobby.com/forum/viewtopic.php?t=4704I also discuss there how to basically set up each output, and even create a "partyzone" that combines all the stereo pairs of the CL card into one kx output.
and will I have to buy amplified speakers? i.e., is the output from the 5.1 card already amplified?
The outputs of the 5.1 card are not amplified. Even if they were, the amplification would not be suitable for a zoning enviroment. You could use amplified speakers. The one problem here is long cable runs of low level audio. If the cables are inadequate, you could get induced noise on the signal. The other thing to worry about is the capacitance of the cable could act as a filter and you could loose the upper bandwidth of the music. To get around that, you could build yourself (or buy) balanced cable runs. Now I'm talking cable lengths greater than 30' (some people have had success running greater than 50'). Not to mention that sort of cable is more expensive than simple speaker wire. Most people will have a multichannel amp close to the source then run speaker wire to the speakers. Big reason besides expense. The signal will not degrade as much. You just have to use the proper guage of wire for the length of run you require.
The big problem with wireless speakers is radio wave interference, and inadequate frequency bandwidth. Being a music lover, neither would do you any good.
Hope this was helpful.