Not to discourage you although any changes you might notice by op amp rolling will be caused by gain differences. Either louder or quieter volume levels if the op amps can affect that otherwise it's just swapping one more than capable op amp for another more than capable op amp. The bandwidth of audio op amps is much higher than required for audio use and so decent op amps are all more than qualified for simple audio use. Is it possible to invest in some EQ/PEQ control?