maybe many of you are not aware that there is a new component from AD, the AD5593.
It's an I2C I/O expander but with the possibility to free configure each of its 8 I/O pins as Digital Input, Digital Output, Analog Input or Analog Output.
"The AD5593R has eight input/output (I/O) pins, which can be
independently configured as digital-to-analog converter (DAC)
outputs, analog-to-digital converter (ADC) inputs, digital outputs,
or digital inputs. When an I/O pin is configured as an analog
output, it is driven by a 12-bit DAC. "
I think it's worth a try.http://www.analog.com/en/analog-to-digital-converters/ad-converters/ad5593r/products/product.html