I build 3 ANK Kit DACs, the 1.1, 3.1 and the 4.1. The 4.1 was heavily modded with all sort of AN stuff. PM me if you are interested in what I did. The 5.1 kit is a great machine, sounds marvellous out of the box.
The 5.1 came out after a year from the launch and major success of the Mentor pre-amplifier, and it has the best parts of that in the DAC 5.1 such as big rectifier tube, shunt power supply, big power serves in the supply, short signal paths, latest Mundorf caps and the option of V-Cap or AN caps. TBH I don't think it can be beat for the price, it is really into Audio Note upper level territory IMO. Amazing sound for the price.