I've never unplugged/plugged a video cable with equipment turned on.
I don't know if it could cause a power/static spike and damage something, or how Windows would handle it.
If your monitor has 2 HDMI inputs you could buy another HDMI cable and switch inputs at the monitor.
You can see if your SRS Amp has multiple HDMI inputs, and if it does use that for switching.
I doubt it does because you said it's older, but you can look and see.
You can buy an HDMI switch (and another cable) to switch between PC and PS3.
Here is an example of an HDMI switch. Newegg.com - Link Depot LD-HDMI-SW3P HDMI 3 PORTS SWITCHES W/REMOTE