Connecting my Apple TV to an HP LCD computer monitor. What about the sound?

I am connecting my Apple TV to an HP LCD monitor via HDMI. The speakers in the (computer) monitor are not very good so now I am looking for speakers that I can use with the Apple TV but also use for AirPlay with my iPhone and iPad. I assume that I can't Airplay video to the monitor and Airplay the sound to somewhere else (?) so I would need speakers that take optical in and also do Airplay. Any suggestions for setup and speakers?