You also need a trio of op-amps to buffer the signal, else the pots add extra loading which will introduce artifacts. EDIT: actually, I wonder whether these ar

You also need a trio of op-amps to buffer the signal, else the pots add extra loading which will introduce artifacts. EDIT: actually, I wonder whether these are source+load terminated signals -- that is very common with analog video signals (e.g. VGA). In which case, if the amplifier the author was using doesn't load-terminate the signals, they will be 2× too large (a factor of ~4.6 intensity) when they reach the ADC. In which case, a ~75 Ω resistor at the end of each wire should do the trick, while also improving signal quality.