[Thulani]

Video it will not be re-encoded if you un-check the "Always encode chapter into I picture" (you find this in the track settings)
By default the LPCM sound it will be re-encoded into AC3 (if i remember well). Just go to Options -> Preferences -> DVD-Video Settings -> For linear PCM use the format below -> choose your settings (this can be done from the track settings too but on the next project it will reset the previous settings so if you forget to manage it will re-encode the sound into LPCM into AC3)