Rupert Hirst has written a detailed article on his AVR V-USB media volume control:
My most rewarding projects are the ones which i actually use. I like my audio gear so, this was the perfect companion project!
On my desk i have a headphone amplifier for my AKG K702’s headphones, below it i have my self built Onixia integrated amplifier for my bookshelf speakers. I have been thinking about making a global volume control for both devices for quite some time… here is the results of my efforts.