I am not sure where you intend to measure and with what? Not at the speakers. If you can measure the outout frequency response of the CD player, analog in this case, that would be fine to see how flat the response, what variations are at what frequency.
Better use a calibrated CD of a known level and porbably measure the ouput voltage too of the player. But, you get FR data in Sound &Video, maybe even in Stereopile too
They tend to measure pretty well.
CD Player Comparison, The Sensible Sound, # 75, Jun/Jul 1999.
CD Player Comparison, The Sensible Sound, # 74, Apr/May 1999.
they compared a RCA, $80 unit against several $1000+ units, DBT, 20 trials, young listeners. Best guess was 12 of 20, not very promising