The FireBall and PowerBall are slightly similar sounding at best. I have owned a PowerBall and always thought the two were essentially the same amp, just the PBall had more bells and whistles. Totally wrong.
Check this clip that is Engl FireBall on left, Bugera 333 on the right, 1-track each @ 100% panning L/R. One SM57 on-axis, edge of dustcap/cone, 1/2" from grill on a Mesa oversized 4x12 with V30s. The clip is of a band I recorded a while back. I like the FireBall a lot more than my old PowerBall and may get one in the future to have sitting here for studio work.
~006