Yes the 4K server needs to handshake to a HDCP 2.2 so it won't work through the HD621 but that's ok to me as I have a 10m HDMI cable running from the 4K server video/Audio HMDI output straight to the SONY PJ 2.2 Input.
The Audio only HDMI output from the 4K server goes into the 621so it's all good.

The PJ upscales any content to 4K automatically so I just have the Oppo set to 'auto' resolution as I just use the Oppo for 1080P content anyway.

It would be great if the HD621 did handle 4K as then I wouldn't have to change the input on the PJ when I want to watch from the 4K server.

Would it be feasible for M to incorporate the new 'HD621' into the 861v9?

Theatre Room: Sony 4K VW500ES, 861v8+ID41, HD621, DSP6000's, DSP5000C, DSP5000's, Oppo 205, Sat STB, XBox One X, Stewart Cinemascope Screen, QNAP TVS 1271U-RP (96TB) with Sooloos/Roon core pkg.