There should definitely be no difference in sound when opening Logic bounces in WaveBurner! Do you hear any difference in sound yourself? As a general guideline, when I mix in Logic intending to perform any sort of mastering for lets say an audio cd afterwards in WaveBurner, I will leave plenty of headroom (-4 dB to -6 dB), avoid any dithering and keep the projects File Format, SR and Resolution intact. All the audio mastering and converting I will perform in WaveBurner and will hopefully notice differences in sound but never prior to that.
Have a nice day!