WiiSXRX is a Sony PlayStation emulator for the Nintendo Wii. Compatibility isn't great, and it hasn't been updated in a long time, but it's still neat. It supports Wii and Gamecube controllers, and loading games from SD Card, USB, DVDs, and Samba shares.
First you have to run the emulator and tell it to generate a config file for you. This should end up in the wiisxrx directory on your SD card, but iirc you can send it to the USB too.
settings>general>Save settings.cfg
The last four options are the SMB-relevant ones:
smbusername is your SMB user.smbpassword is your SMB password. I had trouble with the password I use for Open PS2 Loader (which was already a compromise to work with that), either the 30 character length was too great, or it didn't like some of the special characters.smbsharename also tripped me up. This can't be a path with subdirectories, just the base directory of your share. So you might have to navigate to your ISOs :|smbipaddr is your SMB IP address.