COntinuing the discussion and answering the question...
About the SPI, I feel like digging into the Datasheet of the AVR and configuring every single bit on my own instead of using the Arduino dedicated functions. Of course they are much more user friendly, but I want to learn more about the HW and be closer as possible to it, so i might do the same, I prefer ton configure it on my own.
About the ADC, I have today very good audio results with my 8 bits DAC presented in the links above. Resistors are basic 5% tolerance, so there is non linearities spread among the way, it can be heared, but for a "lowfi but still accurate" project, it's worth it.
I will eventually use MCP4921's for my final Synth Shield, but only for "cleaning" purpose, I feel perfectly at ease with the current resistor based 8 bit DAC. I have not tried higher resolutions though, because of this table you mention.