MX4SIO (Memory expansion For SIO) is an adapter for the PlayStation2 that lets you connect SD cards to the memory card slot.
The MX4SIO can not replace a memory card! Since it is only an adapter and not a converter to make an SD card into the PS2 memory card.
The SD/TF card is not recognised by the console directly. Only specially developed homebrew software can access the SD/TF card, although the software is currently in the development phase (like the OPL).
It is recommended to use the latest version of OPL Minimum version: v1.2.0-Beta-1832-f087feb.7z