Based on what I read of the specs on that projector, I guess the built in 2W mono speakers aren't cutting it? It doesn't seem to have audio-out so you're kinda screwed in terms of hooking anything up directly to the projector for video and sound.
Are you planning on connecting the sound to many different devices (e.g., to multiple laptops that make it into the conference room), or is it going to be permanently attached to a single computer that remains there all the time?
If you're interested in wireless, and you're not going to need to pair it with more than 2 computers (or you don't mind the hassle of constantly pairing), you can go with a Bluetooth audio, A2DP solution. Most laptops have Bluetooth built in, few PCs do so you would need an add-on dongle/card if you want this to work.
The Jambox Big and original size get good reviews. They also have built in microphones, so you can use them for a computer-based conference call, as well. The ad copy for the big specifically mentions conference rooms. Maybe it's what you want?
Not the best solution, but definitely a wireless one.