hi,
Has anyone here ever used PEAQ method to check the quality of your audio wavefiles? As is suggested by its standard, only wave files of 48khz sample rate are applicable to this testing method. As I know, some commercial tools supports 44.1khz as well. Then how about the rest bunch of sample rate, like 32khz? Does it mean PEAQ should not be used in any case other than its predefined sample rate? Thanks.

First take into account that PEAQ has 2 versions Basic and Advanced. Advanced has a bit more correlation with subjective listening test results.
It was developed for 48000 Hz, but Opera (commercial implementation) for example also accepts 44100 Hz. And it is expected that using 44100 Hz shouldn't produce to much differences than first upsampling to 48000 Hz. But in my opinion there are some things that need to be changed and neural network retuned in order to make PEAQ accurate enough for 44100 Hz.
But even after having "good" version for 44100 Hz, don't expect that it will be precise enough to replace your ears.