With vigour (3,4)
(Other definitions for con brio that I've seen before include "vivaciously" , "Musically, with zest and animation" , "(In music) with vigour" , "Energetically" , "In music, with verve or vivacity" .)
(Other definitions for keenly that I've seen before include "Eagerly, sharply" , "With eagerness" , "Eagerly, enthusiastically" , "In an eager manner" , "With enthusiasm" .)