To earn a crust earlier in their career, Mexican guitar duo Rodrigo y Gabriela - that's Rodrigo and Gabriela, for non Spanish-speakers - used to play in hotels. Little did guests know that what they were hearing were often acoustic versions of songs by metal bands like Slayer, Megadeth, and Testament.

"We had to make some money and we didn't have the normal repertoire that hotel musicians have ... so we played a metal repertoire," laughs Rodrigo Sanchez.

He's in Ixtapa, Mexico, a beach-side town he and Gabriela Quintero now call home after growing up in Mexico City and spending the majority of the 2000s based in Dublin.

These two - whose music can be best described as acoustic flamenco metal - might play guitars with nylon strings, and Sanchez especially looks more like a classical guitarist when he plays than an axe-wielding metaller, but their roots are firmly entrenched in heavy metal.

They met in Mexico City in the late 90s when they played in thrash metal band Tierra Acida. Then around 2000, tiring of the local music scene, and keen to expand their musical horizons, Sanchez and Quintero packed their acoustic guitars and headed to Europe.

Also around this time Sanchez said he was becoming more aware of indigenous Mexican music, in particular composer Jorge Reyes, who combines electronic music and traditional instruments. Reyes is one of 11 musicians and bands they pay tribute to on their latest album 11:11 which is out next week. But more on that soon.

"Gabriela and I had a metal band," continues Sanchez, "and we never wanted to sound like older traditional Mexican and Hispanic sounds until I heard Jorge Reyes. This guy was incredible. It's a very ritualistic kind of vibe and he would have indigenous people, like Aztecs, dancing at his shows. He was the whole experience.

"I think he was important for me, and a lot of people of my generation in Mexico, because he gave more importance and exposure to that type of music, and it's pretty stunning music."

Meanwhile, in Europe the pair busked, played hotels, and started getting a steady string of shows. During this time they developed their duelling lead-versus-rhythm guitar attack, with Sanchez's lightning-fast picking and plucking style, and Quintero thumping, tapping and strumming like an all-in-one rhythm guitarist, bass player and percussionist.

"The good thing about us is that we both have different techniques. I cannot do what Gabriela does and she cannot do what I do. That's a good complement.

After releasing debut album re-Foc in 2003, and a live album the following year, their big break-through came with 2006's Rodrigo y Gabriela album, which contained mostly original instrumentals but also covers of Led Zeppelin's Stairway To Heaven and Metallica's Orion.

It proved a hit. I saw them at the Coachella music festival in California in 2007, and a crowd of thousands had gathered at the tent stage where they were playing. This odd duo, who strode up on stage, Quintero with a beaming smile and Sanchez more serious, were a major attraction and one of the highlights of the three-day festival.

"We were just doing something different," says Sanchez of their appeal. "We play festivals all over the world, and everything sounds the same, especially this indie thing. But we are original."

If the self-titled album had an intrigue, and an almost dancey catchiness to it, then 11:11 is more difficult. The 11 songs are written as tributes to well-known people, like Pink Floyd and Jimi Hendrix, and others not so well-known such as Reyes, mentioned earlier, and wild 70s world fusion ensemble Shakti, lead by English guitar player John McLaughlin and Indian tabla player Zakir Hussain.

"These days an album has to be so much more than just the artist and the music that you play. So a tribute to the music that inspired us seemed a fair thing to do ... and hopefully people will discover a whole new lot of musicians they never knew about."

And this time round the album is not confined to acoustic guitars, with the title track (a Pink Floyd tribute) using piano, and an electric guitar played by Alex Skolnick of Testament on Atman.

They also went back to their roots by working with producer Colin Richardson, who has worked with Slipknot, Napalm Death and Fear Factory, and recorded the album as if they were making a metal album.

"It's not the same sort of hooky album as the last but what's important is that we like it and the contribution it makes to music."

Who: Rodrigo y Gabriela, made up of Rodrigo Sanchez (lead guitar) and Gabriela Quintero (rhythm guitar)
What: Mexican guitar duo who play acoustic flamenco metal
New album: 11:11, out September 7
See also: Rodrigo y Gabriela (2006)
Playing: Auckland (venue tbc), Jan 11