Are there some sort of specs that indicate the "goodness" of a DAC? I will of course use the ultimate measure, my own listening experience, but before I shell out a few hundred bucks I'd like to know if there are some measures that I can use to compare DACs pre-purchase.
AFAIK, the precision and noise performance of modern DAC chips is universally beyond the ability fo the human ear to discriminate. (Moore's law and all that). The other electronics in an outboard DAC, if poorly designed, could potentially have an audible effect but it seems unlikely to me except in cases where the DAC is implemented with intentional frequency response deviations (like the 80s era British high end rolloff).
In general with modern systems utilizing digital sources (and especially where one wants to take advantage of digital crossover settings, or room correction software, which can be a great boon, there's no reason to use an outboard DAC. You just push yourself into having to get a receiver or pre-pro that can re-digitize (via an ADC) the signal it gets from the DAC, and then perform its digital work (crossover rolloffs, room correction) and then take the result of that work and send it to the receiver's internal DAC to obtain an analog sound that the amps can amplify and the speakers can play. Unless you choose to be a purist and avoid all processing or prefer to implement crossovers and any EQ using potentially less accurate and potentially noisier analog components, you can't avoid using the receiver's DAC anyway, and you incur the (likely very slight) cost of one additional generation of digital-to-analog-to-ditgital conversion.