Struggling with this one.

The Vertex has no concept of MHR, it just passes LPCM to the HD621 at whatever rate, which is usually 48k or less. If you tick 96k on the HD621 you get MHR or MMHR as a result of the 96k upscale.

Whatever else, the content is de-jittered, if the manual is to be believed…

Lounge: G61RSL, DSP3200, DSP3300, DSW, HD621+Vertex2, SBT, Kef Ci160.
Office: DSP33, D1500, SBT
Archive: 568.2m, 562v3, 562v, DSP3100