I also have a ADC-3100 that I will be selling in the next few months. I was hoping to get quite a bit more than that for it, although unlike the unit you mention, mine is in fully working condition and I also have four HC-15 speaker systems.
I was toying around with the idea of midifying it prior to selling it, but not sure in the end it's worth my time. Any idea what something like this would fetch if it were converted?