PC automation/ relay trip on shutdown

[Thunau]

Hi,
I would like to find a solution to the problem of computer soundcards shutting down with a loud pop.
One of the users of Frequency Allocator software has lost an expensive tweeter when his son turned off the computer before the amps running the tweeters were turned off.

I wouldike to find a solution where the signal to the tweeters goes through a relay, which is powered by a voltage from PC. On computer shutdown the voltage to the relays goes down before the sound card loses power and makes a pop. Could RS232 port be used for that? How about some other 5V output that is common and available on every motherboard?

Thanks