can I use PC onboard audio output

updates: Checked online and here is the reason why answer is no. speaker out is the one with pre-amp. use it as audio input to another amplifier may damage the amplifier . (Use low output may OK, but not right way). Use line out is right way to do. So configure the PC as 5.1 and also connect the line out to whole house amplifier system maybe the right way. Hope my PC is able to provide the 5.1 output and also line out output.

It was posted in 实用电脑 and some other websites. I post here in order to get some more suggestions since so far no comments yet. :-(

Hello, All,
First, thank you so much for any suggestion you can provide to me. Also thank you for your time to read this post even if you do not have any comments.
 I have an existed 2 story house. I plan to use HTD middle level whole house audio system. MC-66
http://www.htd.com/Products/mid-level-whole-house-audio
 it has 6 control sources and 6 zone amplifiers. I plan to use two TVs audio out and two PCs speaker out as source. The PC has onboard audio out, It can be configured as 7.1 output. The PC also has Logitech Z-5500 5.1 Speaker System as speakers. My question is can I setup my PC to 7.1 and use 5.1 to drive the logitech Z-5500 and the other two side speaker outputs connect to MC-66 control source? Is the speaker output good enough for control source? How can I use the PC audio output as source to send signal to whole house speakers?

The PC is over-the-air HDTV.
PS, My PC is MSI 785G-E53, AM3, the audio information I could found is as follow:
Audio
• Chipset integrated by Realtek® High-End Audio chipset
- True Blu-ray Audio Support
- Flexible 8-channel audio with jack sensing
- Compliant with Azalia 1.0 Spec

 Thank you so much for your time and help.