Wii:Wii Dual
The Wii Dual is an internal upgrade for the Nintendo Wii that ads a true digital-to-digital HDMI output. It also ads RGB and RGsB support to all model Wii's and improves the output quality of the component video output.
The board is based off Ingo Korb's GCVideo project, which reverse-engineered the digital chip in the GameCube's component video cables. All GCVideo solutions are _zero added lag_ in both analog and digital versions.
Full Video Review:
Purchase Options:
Wii Dual kits are available directly from the creator: https://shop.dansprojects.com It's a complicated installation, so it should be considered an expert-only install. Pre-modded units should be available for sale as well.
HDMI Options:
The Wii Dual uses a Mini-HDMI jack. I suggest a Mini-HDMI to HDMI cable, but a pigtail adapter will work too: \[amazon\_link asins='B01M1ALRQQ,B00B2HOS08' template='ProductCarousel' store='retrorgb-20' marketplace='US' link\_id='24d26580-8032-4292-8429-33055ddc0d1c'\]
Compatible Wii's:
The Wii Dual is compatible with the following board revisions:
RVL-CPU-40 / RVL-CPU-60 / RVK-CPU-01 (K01) / RVK-CPU-02 (K02)
There are two ways to determine the model. An easy way is to look for a Black, Light Blue, or Red Wii that include the GameCube ports. Unless someone did a case-swap, those will be compatible.
To guarantee compatibility, you'll need to remove the battery (just one screw) and read the motherboard revision. As an example, the one shown here is _not_ compatible: 
Installation
The creator of the project, Dan has posted a detailed installation video. I'd consider this an "expert install":
Case Cutting
The Wii Dual requires modification of the case. If you're a fan of #nocutmod's and preserving the original plastics, maybe consider modding a replacement case and saving the original? There's some awesome clear cases available here: https://xcm.cc/pages/replacement-case-for-wii-console-ii-case
GameCube Support
Some of the Wii revisions that this kit is compatible with are also backward-compatible with the GameCube. Using the Wii Dual will get you the _exact same_ high-quality output you'd get from a GCVideo solution for the GC. It is also equal to the official Nintendo component cables. In fact, unless you use your GC for the Game Boy Interface, you won't even need a Game Cube after this!
Creator Interview
Here's an interview with Dan, the creator of the Wii Dual mod that was condicted shortly before the release. It talks about this, as well as other exciting projects Dan has been working on!:
Conclusion
The Wii Dual is for someone who wants the best quality audio and video from their Wii. You can achieve dual outputs on an unmodded Wii using a component video splitter and you can get HDMI with a YPbPr-to-HDMI converter...but none will look and sound as clear as this.
This is by far my favorite way to play Wii games.
For more information on how to get the best out of your classic game consoles, check out the main systems page. If you're unfamiliar with some of the confusing terms you might hear in the retro-gaming scene, please see the RGB Guide that will walk you through everything you need to know.