DACs should not have synergy with anything. A DAC should be neutral, the better the DAC, the more neutral and transparent.
So "You start with headphones whose sound signature you like" is correct ! Then find an amp that has synergy with your cans - you can ask in the head-fi thread about those headphones which amps work best.
A DAC should be the best DAC you can afford, and of course, that has the outputs, inputs and size that you need. Once in a while, there may be an electrical need for a particular product (such as "so-and-so amp requires a DAC with high voltage output") but that is rare.
A reviewer can truthfully say that an otherwise good DAC sounds "warm" or "bright" or "lacks dynamics", etc. etc. But those are flaws, and should be very slight, they should not be used to match with other electronics.
In the case of the Vali, if you do not have a DAC, then the best choice is a Schiit DAC, because the two products will match visually. As in this picture:
Edited by kstuart - 10/16/13 at 1:44pm