The S.E.X. 2.0 kit came with a pair of inexpensive line matching transformers for output transformers and a plate choke made to match. The current S.E.X. 2.1 kit uses improved Bottlehead plate chokes and output transformers, the same ones we use on the Stereomour 2A3 amp kit. This kit will allow you to upgrade a S.E.X. kit 2.0 to perform much closer to the 2.1 sonically. Bass linearity will be improved by an octave and the amp will sound more dynamic. And of course the kit comes with our usual high quality instructions.