The Cine9 was one of the best CRTs out there (better even than my Barco 812), but even at the time, switching from DVD to real 1080p material it was obvious how poor DVD was in comparison. No way does 1080p on a Sony look worse than DVD on a CRT. If it does, then something is wrong in your chain

Once blu-ray arrived I stopped watching DVD. I'm hoping for a similar experience with UHD. My blu-ray collection is about to become legacy...
Er no, there is nothing wrong in my video chain thanks

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The Cine 9 WAS the best CRT projector available.
Did you ever see a Cine 9 playing a reference quality DVD upscaled by a crystalio scaler to 1080P?
Or are you just assuming what you think the picture would look like?
I recall the Barco 812 had 12" tubes, so at 500 lumens had lots more light output than Cine9, but 2 issues were:
1, huge glass curvature making edge focus poor.
2, line quadrupled wasn't enough. you could still see scan lines.
So DVD upscaled would look far better on a Cine 9. Much sharper image with no visible scan lines.
My real point was that upscaled DVD looked impressive and cinematic on a decent CRT projector, but upscaled DVD looks poor on a modern digital projector.
Also, in a blacked out room, the blacks/contrast ratio/dynamic range and the resulting image depth on the Cine 9 CRT I used to own, still has not been bettered by modern digital projectors such as the JVC, and Sony. They cant stitch the light off completely when black is required in an image. They rely on double iris etc.
I have owned several of the JVC's released over the last 5 years. I only swapped to Sony as it has greater light output more suitable for a large screen.
Anyway back to the topic, a HD621 would need HDMI 1.4 to support 4K at 30Hz, and HDMI 2.0 to support 4K at 60Hz.