Before you give up, try these OPL (press Triangle on the game in OPL):
This is the "Gold Standard." The PS2 was designed with an expansion bay (in the "fat" models) specifically for a hard drive. By using a network adapter and an HDD, games run directly through the PS2’s high-speed ATA interface.
When a PS2 boots a game from a disc, it utilizes the DVD drive's mechanics and the "EE" (Emotion Engine) processor to stream data. OPL works by intercepting these calls. It tricks the PS2 into thinking it is reading from a DVD drive when it is actually reading from a hard drive or USB stick.