I know what you said ..
digital amp == AC07 codec ssytem
it is pure digital and AC97 use delta-sigma D/A
deltaSigma A/D --> Nation semi or AnalogDevice have many paper
deltaSigma -> use C or matlab or hspice behavior simulation
but modulator is switch Comparator , it can simulation by spice , you can find many paper about it , but we usually matleb simulation system , hspice only simulation circuit
delta sigma D/A --> use digital filter --> codec analog chip
codec is Low pass filter