With MHR disabled, was the signal limited, e.g. to 16/48?
I don't believe so, however this was some time ago and my DAC at the time was itself limited to a max of 48k.
What I can say with certainty is that the HD621 will take in 44.1k, 48k, 96k and 192k and successfully down-sample (as needed) for output to a 48k DAC with no MHR encryption for all sources that I used. I.e. including DVD, Blu-ray , DVD-A etc. The lower frequency sources are passed as is, i.e. not re-sampled to 48k unnecessarily.
I can't remember if I tested the 96k output with a non-Meridian DAC. Within config the output rate and MHR are different items, however, one would need to check that they are 100% independent for 96k output.
John