This may not be of any help, and I haven't explored it myself, but if you're using Mac OSX, there's a program called "Audio MIDI Setup" which seems to allow MIDI communication over a network. I imagine there's some equivalent for Windows as well.

pulseaudio should do that !

I set up a linux to windows/ windows to linux network and accessed a soundscape generator on one of the machines through tcp/ip. This solution might be an overkill for you and perhaps not what you want to do but here's the info anyway.

I used the Network library in a processing sketch to connect to the sound generator software. The sketch would then send a simple text command over Tcp/ip whenever it wanted a sound played. Just make a Client object and instantiate it and then use the write method to send the messages. See the Client example.

The soundscape generator was running in python which worked pretty smoothly in both windows and linux.

Here's the link to the soundscape tool http://www.eblong.com/zarf/boodler/

You have to make a listener agent but it is all there in the help. I do recall having to change the way the python setup the socket initially to get it to work over the network and not only for localhost. If you get there and get stuck let me know and I'll dig up the details.

Of course you could equally write a Server sketch which catches the commands from the Client sketch and then plays sounds. I haven't checked out playing sounds from a sketch in linux.