What is the minimum recommended DAC SNR for different modulation schemes such as BPSK, QPSK, and QAM?

Kim,

The SNR requirement is a system specification and is generally not tied to the modulation type.  Different standards will require a different level of bit error performance which will translate to a certain in band SNR requirement.  There will be other transmission specs which will also be important such as meeting the emissions masks - this is related more to linearity of the device vs the noise.

Communications standards discussions and system level design questions are out of the scope of this forum.  If you have a data converter/device related question, we will be able to help you better.

Ken.