Guys we are an NAD dealer the m33,does indeed digitize an analog signal in order to use DiRAC Room Correction for all sources.
so your answer is the analog input will sound different then streaming but if you want to hear the best in analog I would trade in the m33 and go up up to the nad M66 which has a true analog Preamp as well as an improved dac.
Dave and Troy Audio intellect NJ
Nad masters dealer