NIGHTWISH bassist/vocalist Marco Hietala will guest on Dutch guitarist/composer Arjen Lucassen's new AYREON album, "The Theory Of Everything", due before the end of the year.Behind-the-scenes footage from Hietala's recording sessions for the CD can be seen below. Lucassen previously stated about the new AYREON effort: "['The Theory Of Everything' is] going to be a double album, so there is a lot to write! It's extra challenging as well, because lyrically I've left the old AYREON universe behind and have to create a new one from scratch. "I'm really excited about the lineup and how everything is PROGressing so far. There is physics involved, but mainly it's about human relationships and the emotional costs that come with treading the fine line between genius and madness." AYREON's latest album, "01011001" (2008), sold 1,400 copies in the United States in its first week of release to debut at position No. 32 on the the Top New Artist Albums (Heatseekers) chart (which lists the best-selling albums by new and developing artists, defined as those who have never appeared in the Top 100 of The Billboard 200). AYREON's 3CD + DVD compilation album entitled "Timeline" came out in November 2008. The set followed the thirteen-year evolution of the AYREON sound from the 1995 debut "The Final Experiment" to the release of "01011001". In addition to selecting tracks from the existing AYREON discography, Arjen also wrote and recorded a new AYREON song exclusively for "Timeline". Titled "Epilogue: The Memory Remains", this previously unreleased nine-plus-minute track introduced AYREON fans to the clear, powerful voice of Jasper Steverlinck (ARID).