Right, so back then if you had titles on an emunand u couldn't launch them via a usb loader unless u created and launched a forwarder iso. Now that last step is not needed, simplifying the process.
Nothing you do will retrieve your old content, unless u find your old content somewhere on a drive or SD card. If u had purchased games from the official wii shop channel, that's a different story.
Create an emunand, either by dumping your own using bootmii and converting the nand.bin to an extracted folder format using showmiiwads (under tools). Then add content to it by using showmiiwads' showmiinand view/mode, drag and drop wads/content you want to install.
Alternatively you can build a minimal/fresh emulated nand using modmii, boot into it one time using neek, then add content to it using showmiinand (or modmii's emulated nand modifier).
Once you have a working emunand, just adjust usbloader gx's settings, pointing it to the directory you have the emunand, and change the view to show emunand content
@godreborn can perhaps describe his optimal emunand/neek settings for gx. Most titles won't need anything special, but some need full neek mode, and iirc godreborn has suggested installing those to 2 emunands. He'll be able to better describe the procedure