Grails play Local 506 Thursday, April 21, with guitarist James Blackshaw at 9:30 p.m. Tickets are $10–$12.

“If music was a lady,” Emil Amos says of his Portland, Ore., band Grails, “we would fuck anything that moves.”

With Grails, the analogy isn’t just provocative hyperbole. The decade-old instrumental rock actincluding founding members Amos (Holy Sons, Om) and Alex Hall, and now with Zak Riles (M. Ward’s second guitarist) and William Slatertakes a notoriously promiscuous approach in a genre where clichés and rote formulas abound like the waves of swell-and-release crescendos so many post-rock bands typically chase.

But instead of reading like rootless dabbling in various instrumental rock fonts, Grails’ current collage creates a spellbinding, labyrinthine journey backward and forward through time. Middle Eastern exotica swirls into sludgy stoner rock riffs. Desert-baked noir-scapes lift off into synth-fueled space rock. Elemental drones contrast with trip-hop beats and modern chop-shop sampling. Theirs is an evolving maze.

“We’re trying to pull our template’s edges further and further out towards a more lawless experimentation,” Amos says of every record, “while developing the most elaborate compositions we can manage to write.”

Grails’ early recordings leaned heavily on violinist Timothy Horner, together tilting toward Dirty 3’s dusky mirages. When Horner left, the band incorporated heavier and more gothic elements, especially with the mid-decade series Black Tar Prophecies, a collection of splits and EPs eventually packaged together in 2006. Grails’ restlessness inspired a turn toward Middle Eastern modal explorations on 2007’s Burning Off Impurities. But the next year’s Doomsdayer’s Holiday was the heaviest Grails record yet, an ominous “slouching toward Bethlehem” beast impressive for its nuanced power and dynamism. The well-received record raised Grails’ profile even in the metal community.

Rather than reiterate the formula, the latest releasethis year’s Deep Politicsfinds the quartet heading off in yet another direction to explore the relationship between film and music. Elaborate and sensual string arrangements by Timba Harris haunt the slinky “Daughters of Bilitis” and nod to French film composer Francis Lai. “All the Colors of the Dark” recharges the Spaghetti Western-flavored composition that Ennio Morricone understudy Bruno Nicolai wrote for the ’70s psych-horror flick of the same name. Even when the connection isn’t apparent, Deep Politics is the most visually evocative of all Grails’ LPs.

But applying the term “cinematic” shortchanges the band’s approach. What attracts Grails to film music, says Amos, is that it “forces a different kind of listening,” one that uncovers a “black hole of ambiguity” that can be exploited to expose feverishly bizarre states of mind. If the audience agrees to get on board, Amos says, “the entire ceiling opens up of what’s available to express.

“We’ve been trying to live on this idyllic philosophical island that film music suggests while imagining that other people might care if we could build a ladder out to a new musicology,” he continues. “Unfortunately, they just keep calling it ‘cinematic rock,’ which can partially drain a raw expression of its power.”

If Grails’ music is the soundtrack to anything, its dark tempests read like a bulwark against an impersonal cultural wasteland where commodification “transforms everything and everyone into a product,” Amos says, all to decimate “the concept of true communication.” Grails’ influences may come largely from artists who have turned their backs on cultural mores to create something unique, but for Amos and Grails, that isn’t enough anymore.

“Conscious integration and awareness of what needs to be posited in your time” are now the ultimate goals, he says. “Truth and the possibility of true communication are the last vestiges of a reason to continueso you are forced to sludge further towards the dimming evolutionary light and ignore the bodies piling around.”