Octahedron (Warner Bros.)...It was pretty easy to find fault with the first four Mars Volta albums. All of them were basically the same dense slab of sonic masturbation — equal parts aural bliss and epic clusterfuck. And yet, the El Paso-based progressive rock band continued to sell more records and play to ever larger crowds, while defying current record-industry practices in about a hundred different ways. Octahedron, the band's fifth full-length, has got something going for it that the others didn't have:…