How does a band that hasn’t released music since 2004’s eMOTIVe, and has played few shows since, sell out the 9,450-capacity Red Rocks Amphitheatre? The simplest answer may be that the band features Maynard James Keenan, the lead singer of the rock band Tool. The cult-like following Tool has garnered during its 20 years certainly does spill over into A Perfect Circle’s fan base, but don’t let that fool you. A Perfect Circle is not some kind of “side project” for Keenan to indulge in his musical guilty pleasures. A Perfect Circle is its own entity with a sound very much different than TOOL. This is because the centerpiece of A Perfect Circle (APC) is the guitarist/singer Billy Howerdel.