The 256 value limitation for the analog out is the reason to choose a DAC that kan be serially controlled. That way you are only limited by the capability of the DAC.
The MAx536 has 12 bit precision. That will give you 4096 discreete values. If your synth use the standard 1V/octave over a 0 -10 volt range you will have a little more tha 409 "steps"/ octave or 34 "steps" for each key in the octave. This should be enough even to make pitch bends with out anoying stepping of the pitch.