Mid Range Remote Volume Control

Good Afternoon,

My name is Josh. I am the owner of the new outdoor product company Juvie Juke Box. We make electronic snow goose callers that our customers can use during special seasons in the US and in both the Fall and Spring in Canada. We currently have our units running off a 400-800w marine grade amp, which gets sound from an MP3 player via AUX cord. We currently are using an ON/OFF remote that cuts power from the 12v battery to the amp.

We have searched high and low for being able to adjust the volume wirelessly and have come up with nothing but frustration. Lack of knowledge in this department is mainly to blame. I have seen coyote hunting callers, mainly from the company FOX PRO with the ability to adjust volume from up to 300 feet away but can not figure out how. We have looked at a few items on ebay that I'm thinking may accomplish this but seeing as they come from China or Japan have little to no information on the range or instructions on how they work? This is what I am referring too,

http://www.ebay.com/itm/9V-Infrared-Remote-Control-Volume-Control-Board-ALPS-Pre-AMP-Motor-Potentiom...

My question is does anyone know of a way to accomplish this? And if so, would anyone be willing to help us get one working?

Thanks!