No adaptors but You can buy usb sensor bars on amazon http://www.amazon.com/Nextronics-Sensor-Bar-USB-Nintendo-Wii/dp/B001UAAX60/

If you like throwing batteries away you can always get a wireless sensor bar too.

The sensor bar is just an array of infrared LEDs. Any cheap USB IR bar should do the trick.

This is the one I use - amazon.com/gp/product/B001UAAX60/

1, I do use a real Wiimote to play Wii games, but not specifically Mario party 8.

2, I have official RVL-CNT-01 Wii motion plus controllers. Motion plus does make a difference, especially if it is a RVL-CNT-01-TR model. That model communicates to the Wii/Dolphin differently, so it is harder to connect them. Third-party Wii controllers also have trouble connecting to Dolphin. Here is a guide on how to connect the TR Wii motion plus controllers: Dolphin Emulator - Wii Remote Plus (RVL-CNT-01-TR) Connection Guide. You can use third party controllers and TR Wii motion plus controllers if you use Bluetooth Passthrough, although it will require extra hardware.

3, sensor bars are pretty simple. The sensor bar doesn't communicate to Dolphin, all it does is light up a few IR light sources on both sides, which the Wii remote uses to determine its location. I would recommend this cheap one I bought, but it doesn't really matter all that much. One thing to keep in mind is that you can use an original Wii sensor bar, or even two candles, although it isn't optimal because of the risk of spilling wax on your setup.

4, you will need Bluetooth no matter what controller you want to use. If you already have Bluetooth, and an official non-motion plus Wii remote, or an RVL-CNT-01 Wii motion plus controller, you can simply connect by using the option to emulate the Wii's Bluetooth adapter and setting the controller as a real Wiimote. You will also want continuous scanning on, so all you have to do is press 1 and 2 on your Wii remote, and it will connect.