I’ve found this nice article on op amps for audio applications: Op Amps: Myths and facts. It not only gives some information, why there should be no audible differences, but also explains, why there may be audible differences if you simply replace an op amp by a “better” one. That does not mean, there is no need for high-quality op amps, but you should think which characteristics are necessary in which part of your circuit. If you don’t understand how a circuit works, try not to improve it by replacing op amps by more expensive types.