Dudes can play. Speedy fretwork, slashing synth runs, nuclear-option drumming, Avant Guardian have the chops to impress the prog-metal crowd. They put it all out there on “Zero Sum,” stuffing everything they’ve got—classical piano & violin, tricky time sigs, flamenco guitar and jazzy keyboards—into one ambitious opus. The less cluttered “Identity Crisis” and “Inner Purpose” exhibit a similar handicap in that lead vocalist Adam Denlinger, despite the operatic passion he invests in every word, lacks the tonal resonance that’s needed for this music. He has a decent voice, but it is one-dimensional. Also, it doesn’t help that the songs’ messages of desperation are quite similar to each other.