Re: American "voiced" amp, with British "voiced" extension cab???
To answer your early Brit vs American amp definition... This is applicable for the HI-FI corfsniffer and the guitar amp side of things... American is bright, immediate, upfront, exciting. British, in relation, is darker, mellower, laid back, bit more linear.
See, how the corksniffer comes out when talking about these nuanced things. Ever heard wine heads talk about the bass note and overtones of burnt rubber and chocolate, with a nose of ripe raisin?