HDMI Audio needs to be set to LPCM in the player config, you can confirm this by pressing Fn+Display a few times on the MSR, I'm pretty certain a 568.2mm will show Mov6 if the player is decoding DTS-MA to LPCM.

If it is decoding DTS-MA to LPCM, I would check the connections on the HD621 and the 568.2mm are seated properly.

Mark
G68, baby Genelecs, Humax Foxsat, Oppo+Vanity93, Toshiba HD-A35, Pioneer CLD-925 + Meridian 519, various other random bits and bobs
Got a black G08.2 you want to sell?