You didn't mention which Ultra model you have (there are many: 4640, 4660, 4661, 4662, 4670, 4800, 4801, 4802, 4850): Settings/System/About
There are differences in optimal settings as well depending on whether the model has a Dolby decoder.
For a 4640, 4800, 4802, and 4850 you need to change: Settings/Audio/Digital output format = Passthrough
For all other models (4660/4661/4662/4670/4801) you can leave Settings/Audio/Digital output format = Auto
For ALL player models (including non-Ultra models) you need to disable all sound modes including Volume Leveling and Dialogue Enhancement which are enabled by default in most firmware versions: During playback Options (*)/Sound settings/Customize sound modes/Volume Leveling or Dialogue Enhancement = Off