Keep it on the down low. That's how they do it in the underworld, and that's how they did it on the "Underworld" soundtrack.

For the past six months, Danny Lohner -- a producer, multi-instrumentalist and member of Nine Inch Nails -- has been quietly bringing together artists like David Bowie, ex-Limp Bizkit guitarist Wes Borland, Filter mastermind Richard Patrick, A Perfect Circle members Josh Freese and Maynard James Keenan, and Red Hot Chili Peppers guitarist John Frusciante.

"We were basically trying to put together the most crazy combination of people who had anything to do with really cool, darker rock," Borland said.

The guitarist appears on the soundtrack as part of Damning Well, a supergroup of sorts that also includes Lohner, Freese and Patrick -- whom Borland had earlier hooked up with to record a song intended for either the soundtrack of "The Matrix Reloaded" or "Lara Croft Tomb Raider: The Cradle of Life." That song never surfaced, but the Damning Well's "Awakening" is one of 19 tracks on the soundtrack to "Underworld," a vampires-meet-werewolves flick starring Kate Beckinsale (see [article id="1456934"]"Kate Beckinsale's Next Film Mixes Vampires, 'Matrix,' Leather Pants"[/article]).

Consider the pedigree of Damning Well -- a past that includes work with everyone from Bizkit, NIN and the Vandals to Evanescence, Avril Lavigne and Mondo Generator -- and you've got one of the most intriguing combinations since Travis Barker and Tim Armstrong teamed up for the Transplants.

The same holds true for the bulk of the "Underworld" soundtrack, due September 2. "Bring Me the Disco King (Loner Mix)" pits Bowie with Frusciante, Tool/APC's Keenan, singer Lisa Germano and actress Milla Jovovich. "Pucifer" is a Keenan/Lohner joint, while the "remix" of APC's "Weak and Powerless" is more a revision that retains Keenan's vocals but adds new music by Borland, Lohner and Freese. New tracks by Skinny Puppy, Helmet's Page Hamilton and Concrete Blonde's Johnette Napolitano also appear.

"It's just a bunch of unusual things that you don't get to hear very often," Borland said. "It's like Lollapalooza '92," a reference to the lineup that paired the Chili Peppers and Ministry with Ice Cube and Pearl Jam.

Borland said the soundtrack's production was more fun and relaxed than most albums because much of it was recorded in the artists' home studios, without the intrusion of handlers and record-label execs. Works-in-progress CDs and Zip disks were taken from house to house and augmented at each stop. When someone couldn't track their parts locally, as was the case with Bowie, they e-mailed their files to Lohner. It all made for an experience that was closer to a group science project than a compilation album.

"We all kept parking behind each other," Borland laughed. "All these cars crammed into this little driveway. It was just a trip going through that every night. Everyone was helping each other out, too. Like, 'John needs you to run an errand real quick' or 'You're blocking Milla's car in, you gotta move.' It was great having no bullsh-- around. Just a bunch of people getting to know each other and hanging out. And listening to what one person was doing and going, 'Oh, I can add to that' or 'Why don't you do this?' "

The home-studio, DIY approach also explains how the project was kept under wraps for so long. It's rare that a member of a multiplatinum band can moonlight with another project without anyone reporting on it, but it actually happened when Amy Lee took the mic. The Evanescence singer was set to appear on two songs, though her contributions had to be scrapped because of record-label red tape.

"The whole thing was kept very private," Borland explained, "and not even intentionally. When we've spoken casually about it, they're like, 'Oh, I haven't heard anything about that. Weird that there's been no gossip about it.' Until now."

"Underworld" soundtrack track list, according to Lakeshore Records: