Just upgraded two Oppo BDP-83s with BDP-103s. The 103 outputs 4k authored content and upsamples 2k to 4k to a 4k display. An HD621 supports HDMI 1.3, and with the HD621 firmware upgrade, supports 3D over 1.3 compliant HDMI cables.

I puzzled over what it would take to future proof my system for possible 4k compatibility. Since I use their cables, I went to this Blue Jeans Cable web page to learn more about HDMI 1.4 compliance.

The gist of the information is that a true HDMI 1.3 compliant connection also is HDMI 1.4 compliant. Since the HD621 video output is a pass through, it seems that the 4k upsample (or 4k authored content)from the 103/105 would pass successfully through the HD621 to the 4k compatible display as long as the HDMI connection is 1.3 compliant.

Someday, if 4k material becomes mainstream I'll be able to report on the validity of my presumption. Until then, this is my two cents worth.

Tim