I generally post schematics of what I do, I just didn't get around to it in the case of the 8-channel volume control. It has some complications anyway because it incorporates the touch-sense functionality.
Towards the end of this thread:-
http://www.head-fi.org/t/586042/what-i-did-next-with-texas-headamp-chip-a-digital-control-desktop-portable
...you will find a schematic for the amplifier using the 7-segment displays, TPA6120 headphone amplifier chip and PGA2320 volume control. There's a link to a high resolution copy of the schematic. The processor is a PIC 16F887 and regular push-switches are used..
There's also a copy of the code for the same processor to drive the PGA2310 in the parallel NE5532 amp on the webpage. The only difference is that the NE5532 amp has 2 displays for left and right channels, where the TPA amp just uses the decimal points to indicate left, right or both channels controlled.
You should be able to figure out the principles from these, your design will not be identical in detail to either of mine. You'll have to think about whether you want to have independent control of each channel, and how you'll deal with displaying the status of each if you do. I just produced a technology demonstrator for the touch sense screen and drove all 8 channels in unison. I posted pictures on diyaudio but it didn't get a lot of interest so I moved on to building something new. It's a shame in a way because the touch-sense screen is cheap to implement and makes an attractive fascia. I abandoned it for the TPA amplifier because it needs the processor to be running all the time and I wanted to be able to put the processor to sleep to save battery capacity.
The real issue with the PGA volume control chips is the PCB layout. You have to get it right or you can end up with digital noise on the audio, particularly when changing volume. I had to redesign the TPA6120 PCB to get rid of it, although there were no problems with the NE5532 amp. Somebody on diyaudio was complaining about problems with regular audio noise too (hiss), but I didn't have any problems with that.
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