I did that and seem to have corrected it.
The Sound Setting "Default Format" was set to something not default, 16 bit, 96000 Hz.
With it set to default DVD quality it now seems to work fine.

Main: Marantz Cinema 50, Meridian 271, DSP7200.2, DSP5200HC, DSP5000 rears, Meridian 210.
PC/Headphones: Mytek Liberty II, Sansui CA-F1, Sansui B-2301, Sennheiser HD800, Kef R3