About the only investment as fiscally risky as opening a Broadway show is opening a restaurant. So the current crush of Rialto types backing projects that combine the theater biz with food service have their work cut out for them.This summer saw the launch of 54 Below, a supper club/cabaret space from producers Richard Frankel, Thomas Viertel, Marc Routh and Steven Baruch (“Hairspray,” “The Producers”). With a full bar and dinner service, 54 Below, located in the basement of Studio 54, caters to the theater crowd, putting legit names onstage (so far showcasing Patti LuPone, Ben Vereen and Brian D’Arcy James) and hoping to pull in Broadway denizens for post-performance nightlife. Also this summer, the buzzy theater-dance-installation hybrid “Sleep No More,” an environmentally staged noir take on “Macbeth” that unfolds in three adjoining warehouses in Chelsea’s gallery district, opened a bar on its roof. The complex also boasts a fully equipped kitchen, so a restaurant seems a sure bet for the future. Such projects might look crazy from a financial standpoint. But to hear producers tell it, they sure are fun. 54 Below was inspired in part by the producing quartet’s experience working on the 1991 comic musical “Song of Singapore,” for which they created a nightclub space with food and drink service that complemented the show’s 1940s B-movie spoof. “It was not successful financially,” Frankel admits. “But we had a ball.” The fun of it is the major draw for investors, he adds, noting that raising money for 54 Below — which cost “a few million” to launch, somewhere in the neighborhood of a big play — was a breeze. “Everybody wants to own a bar,” he says. Endeavors such as 54 Below and the “Sleep No More” bar, dubbed Gallow Green, also mark legiters’ growing interest in experimenting with ways to expand on the traditional theater business. Randy Weiner, one of the three principals of “Sleep No More” producing org Emursive, has been combining theater and nightlife for more than a decade, starting with the successful and long-running nightclub staging of “The Donkey Show” and, more recently, helping to launch a performance venue-cum-bar at Cambridge’s American Repertory Theater. “All these theater people are looking for new artistic outlets and new revenue streams,” Weiner says. Legit contacts are often tapped in the creation of these new spaces, as was the case with 54 Below, designed by Broadway mavens John Lee Beatty and Ken Billington; and Gallow Green, crafted by Punchdrunk, the troupe behind “Sleep No More.” On the restaurant side, Danny Meyer’s Union Square Hospitality Group was consulted for 54 Below, while David Wondrich, a rock star among cocktail cognoscenti, created the Gallow Green drink menu. But meshing the theater and restaurant businesses involves a lot of moving parts. While 54 Below hasn’t quite caught on with the Broadway crowd as a post-show watering hole, Frankel says it’s gaining steam. He adds that plans are being laid to launch a pre-theater dinner service for patrons not attending the show that night, while also staggering meal reservations to avoid getting hit with a 7 p.m. rush in advance of an 8 p.m. cabaret. It’s the kind of logistical work that not only aims to keep the place buzzing with consistent activity, but also has to be done to maximize earnings from a space that seats only around 150. Despite the risks, producers see the move into food and drink as a logical step into a nightlife scene in which a show is just one stop in a longer evening out on the town. “You really feel like tourists want to extend their evening, especially after 7 o’clock curtains,” Frankel says. That doesn’t just go for tourists, Weiner notes. “You go see a show, you want to go to a restaurant or a bar afterward to talk about it,” he says.