I have both the SEX 2.0 and 2.1, they are very fun to build, the step by step assembly instructions are almost moron proof. The sound quality is fantastic! I have demonstrated the amps in over a dozen audio shows and they always receive great reviews. Some advice, read the assembly manual before starting anything, and take your time building the amp, you do not need to set any land speed assembly records. Build the amp in stock form first, use it for a while then add the C4S board and or change the caps. You will be very surprised how nice two watts sound. As a headphone amp they will power most power hungry phones. For additional info please check out the Bottlehead forum. Later on you can build their Moreplay preamp. There is a saying, "music sound better when you build it yourself", the quote comes from Dan the CEO at Bottlehead.
Here is a pix of my 2.1 amp: