The background
This project is not suitable for a newbeginner, but if you only have a soldering iron with a very fine tip and you don't tremble and have a good pair of tweezers, it shouldn't be any problems to succeed. This amp is not very hard to solder, yes I'm not kidding and it's really cool, not common DIY stuff!
I have made this amp purely for my own pleasure but if someone wants to build it (and is skilled enough), please go ahead. This type of amp is very fast, by nature. The amp consists of three main blocks, input buffer, the amp itself and the output buffer is called "diamond buffer" but I don't where the name comes from. I have also seen the name "Jung Super Buffer" (from his article). Many IC's have this diamond buffer LT1223, BUF634, LME49600 and many more.
This headphone amp can also be used in a preamp as line stage with or without gain, as buffer for DAC's and CD-players.
There are lot's of good info out there on this subject buffers and current feedback amps. Walter Jung has written a couple of good articles and one of them is about this particular buffer. In fact his article is THE best for a normal DIY'er. See references here.
Since many years back I make SMD designs at work so I know about the good properties. One of the real important benefits are the compactness and the good HF performance. You'll get good performance of the passive parts way above 100 MHz and this ensures extremely high performance in the audioband. A man from Slovakia has done some measurements and they indicate distortion numbers down to 0.00046%! Incredible, isn't it, with a design consisting of 2 cents transistors! I can confirm that the performance is way better than my soundcard, 0.0078%.