They may be the only genuine power couple in the South Korea film biz, but Eun Lee and his wife Jae-myung Shim, founder-owners of Myung Film, have handled their commercial and artistic success with grace, class and humility.Myung’s “Joint Security Area,” a DMZ-themed, comedy-drama, released last fall ranks as the all-time highest grosser in South Korea. The film is now poised to take on the neighboring Japanese market on May 26, becoming the first Asian import to open there with a wide release on 280 screens. But while Lee and Shim are naturally anxious to see whether “JSA” will match the Korean B.O. success, producing blockbusters is hardly Myung Film’s raison d’etre. Their follow-up projects are all much smaller personal films — quite a contrast to the current frenzy in South Korea where investors are throwing money at high-budget film projects, many with first-time directors. Since its establishment in 1995, Myung Film has developed a steady reputation for producing high-quality work. Past projects include black comedy, “The Quiet Family,” (1998), intense marital drama “Happy End” (1999) and steamy sexual intriguer “The Isle” (2000). Almost all their works have garnered notice on the international film fest circuit. For Lee and Shim, themselves, film is pretty much a 24/7 endeavor. “We don’t talk about much else,” says Shim, who got her start in the business through marketing at a leading Seoul theater.