An original PS2 game of your PS3 region must be used before using the switch. Once this is done, you can then play and region PS2 games. I have a Jap PS3 and have now bought a Jap Devil May Cry for the PS2 as this has a large TOC so will play most dvd5 discs.
I am currently using a Jap version of The Bouncer but with that only being arond 2.5gb in size, I can not load backups that are above this size. Hence the reason for buying DMC.