Volume control from headphone jack

I have a pro 106 utilizing an external speaker from the headphone jack. I also have a 197 utilizing the ext. speaker jack with a remote speaker. I want to control the volume of each speaker separately at my desk and not the scanner itself. Was wondering if the following item will do damage to the scanners.



Thanks much



AUVIO Volume Control Cable for Stereo Headphones : Headphones | RadioShack.com