It takes an aircraft-carrier of a release such as Live at the Beacon Theatre to remind us just how unique the Allman Brothers Band always was and still is. Traditionally a byword for down-home R&B/country blues-rock, the reality is that the band's gigantic sound is almost a musical form in itself. Make no mistake, the Allmans are still making big music, now with a two-guitar front line as well as their trademark two-drummer rhythm section (augmented these days with an additional percussionist),...