Check the
review index for measurements. If you want to connect the CD player to it you'll probably need an external DAC instead of a hat as very few of the hat DACs have a coax or toslink input.
Linear PSU will probably make no difference to the output. Almost anything with a single 5V supply will be using an internal switching regulator to generate a -ve voltage for the analog output stage anyway, and will have internal regulators suitable for the expected power supply conditions.
For the software side, all the usual Pi software options are capable of delivering the bits to the DAC unaltered. The choice is really about getting an interface and set of features that you're happy with.