Sound Settings for Dual Monitors

I just purchased two new ASUS VX238 monitors which come with internal speakers. I have connected the monitors to my pc via HDMI cable on one and DVI cable on the other. I connected the speakers of the monitors using a Y-cable connected to the audio jack on the back of my pc; connecting each of the green speaker cables to the Y-cable. (see links for photos).

https/www.dropbox.com/s/cvvfj4byrztvtq8/Y-Cable.JPG?dl=0
https/www.dropbox.com/s/xmbnttgmca5g16g/Audio%20Jack.jpg?dl=0

Unfortunately, I am only able to get sound out of the monitor with the HDMI cable, which makes sense as HDMI is the only cable that carry’s sound. To review sound settings, I right clicked on the speaker icon in the Windows taskbar and chose Playback Devices. Here I noticed three options: the two monitors and the SoundMax Integrated Digital HD Audio options (see link for photo).

https/www.dropbox.com/s/u4tlb6k3jzt78px/Sound%20Menu.JPG?dl=0

I’m assuming the SoundMax is the default sound driver that came with the PC. The properties of each of the three devices show that all are enabled. I’ve tried disabling both of the monitors and keeping the SoundMax enabled with no success. And then I tried disabling the SoundMax and then enabling the two monitors without success either.

This leads me to wonder… Is there any way to set this up so that sound comes from both monitors? If so, what am I doing wrong?

Any help you can offer is appreciated. Thank you, Kara