Stream sound from computer to computer

trivial option — enter mstsc, it with sound ;)

1. put a remote administration program (Yes, probably, and built-in "remote assistance" use)
2. in the wood the card to the computer, where it is necessary to listen to the sounds, put the recording with the line out
3. connect the program to the computer, turn on the stream from the microphone
4. ???
5. PROFIT

pulseaudio can. googling pulseaudio windows

Wire jack-jack, one stick into the exit columns on the other to line in.

Task, by the way, in spite of its plainness is very difficult.
At the time, was decided by the organization on a single computer broadcasting on the local network (see the Winamp side). But you need to spend time on setting to ensure the necessary level of synchronization.

Try replacing the Wi-FI network on regular cable. Perhaps it's a problem with pulseaudio.

You can try machines to connect via bluetooth — it can introduce a stereo system.