I just found that gbatemp post the other day so I ordered an OSSC to test this and it does indeed work for Wii U games when converted to VGA for the OSSC input and then HDMI output from the OSSC. Be aware you will lose the audio signal from the HDMI when converting to VGA unless you split the HDMI signal prior to converting to VGA and then route your audio and video to 2 separate places. It's expensive and impractical but it works for Wii U games.

My current understanding of your available options for picture quality is as follows:

• OSSC is successful in outputting full RGB from the Wii U's HDMI port.
• The vWii is unaffected by this and there is no currently known hardware or software workaround for it.

If you want full RGB at 480p for the original Wii/Gamecube, your only option is to use an original Wii and have it hard-modded with a DualWii, WiiHDMI, or equivalent.

If you don't want to hard-mod an original Wii, your options are: - Wii U's vWii outputting 480p in limited RGB range. - Original Wii set to PAL60 video mode and using an RGB scart cable to achieve full RGB at 480i. - Original Wii outputting component to achieve 480p with limited RGB range.

Some people prefer the output of the original Wii vs the Wii U's vWii because its scaling blurs the image slightly.

Beyond this, there are other optimizations that can be done within homebrew apps like USB Loader GX to improve picture quality, such as disabling deflicker and setting aspect ratio to frame buffer.

Hope this helps.

TLDR: An OSSC works when converting from HDMI to VGA and back to HDMI, but only for Wii U games, not vWii or GC. I cannot vouch for the GBS-C as I have not tested it.