That's not exactly what I had in mind. If you create two AFNI BRIK files from the same Philips datasets, you can do a simple diff on the .BRIK files to see if the binary data differ. You can also use 3dcalc to calculate the difference between the two datasets and look at that in the AFNI GUI.
If the two are determined to be different and if you know the slice timing (alt+z), then you can use 3dTshift to correct and see if the PAR/REC-source dataset then matches the NIFTI converted dataset. Philips support can also answer specifics like this if you are using their software to convert the data.