When you say the video outputs are "set correctly", can you be more specific? Virgin 4K help is worth a read, many people have reported the best results from having 2160, 2160p passthru and 1080p selected.
You've mentioned about HD sports channels being poor - again, which ones?
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Have you tried experimenting with the different V6 formats?
I had mine set to 2160p, 2160p passthrough and 1080p which I thought gave a good picture, however I now have it set to just 2160p and leave my TV upscale the other formats and I believe I now have a better picture.
You could also check your TV settings, most have different modes such as a Sports mode, Dynamic, Natural, Cinema and Game.
I have my TV set to Sports mode but do change it depending upon the programs I'm watching.
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