@Greg
I think there is some confusion here (0 db is not an spl level) please read this
http://wiki.jriver.com/index.php/VolumeNow maybe I don't get your system, but either you have a system with active crossovers; bi-amped or better; using JRIver as a preamp; or you simply have active (powered) speakers or monitors, and you are using JRiver as your preamp -- regardless both are going to an external DAC. If there is no analogue volume control in your chain it all depends on the power of your amps and the efficiency of your speakers.
eg. lets say you have a couple of Classé monoblocs outputting 600 watts going into highly efficient speakers like small Klipschs -- your 80 setting might blow them apart. Or you have a NAD receiver putting out 50 watts a channel feeding top end B&Ws -- 80 might not even be enough to move the speaker membranes. It depends, there has to be a reference level ... like what does 80 represent? You have a lot of variables to play around with. Start up volume can be important too See the bottom of the page linked above on calibration
Now if you have an preamp in the chain somewhere or can control the volume of powered speakers, that could change how things are set up.
Also using windows system volume again, not sure this is the best choice, pretty dirty in my book; internal volume is generally what you want ot use (or disabled volume if you can control the volume after your DAC??). I normally set bitstreaming to none, personally