I was thinking of getting a extra box with a Allwinner chip, so I have all flavors of boxes (looks like H6.. series is best ?)
Yes, H6 is the best.
I was wondering if this new passthru feature you are testing also works thru the boxes s/pdif (optical or coaxial) outputs ?
I tested passthrough only on HDMI, but in theory it should work also on SPDIF. It's currently enabled only on Beelink GS1 (talking about H6). I have to check if my Tanix TX6 has it...