The general discussions appears consistently to miss the point. Toast is SUPPOSED to convert 48K files to CD audio (44.1K) on the fly. It did so without incident prior to Leopard. Now, not so much. As our friend has faithfully and repeatedly described, bringing an audio file recorded at 48K sampling into Toast version 6.0.7 through 6.1.1 (for audio CD burning) creates distortion reliably. I doubt that Toast 7 fixed it, though 8 may have (late enough for testing with Leopard). Note interestingly that Toast 6.0.3, 48K files brought in for audio CD burning will not distort, but oddly, files brought in that were exported at 44.1K won't play (preview) in Toast! So one workaround here would be to go back to Toast 6.0.3, which appears to be free of the distorting problem (when converting 48K to 44.1K on the fly, as it should do), but the down side is that you won't be able to preview 44.1K files in the earlier version of Toast. NEITHER of these problems occurs under Tiger, so this is definitely arising from something having to do with Toast on-the-fly conversion that's broken by Leopard.
Good luck to all.