What is your current digital source, and what are you trying to achieve? You may be surprised at just how subtle the audible differences are between a good (newer model) stand-alone CD player and that same player run through a good external DAC. As with most high-end audio upgrades, the issue is one of investment vs return, and beyond a certain point, the return on investment begins to diminish. If you already own a good CD player and your system provides a good natural soundstage, good imaging, realistic timbre and satisfactory bass response, then the DL-III may not add much other than slightly enhancing those characteristics.
I spent about $1,600 on the Stage IV Cullen DL-III and my return on that investment was in fact subtle. I can hear a difference, but it is not a bowl-me-over difference. The bass response, that was already quite good, is now more controlled (in that there is slightly less bloom) there is not greater frequency response, simply a bit more control; the soundstage, which was already quite good, is now a bit bigger (it opened up more) I can hear it when doing A/B comparisons its real, but without doing A/B comparisons I doubt that Id really notice; the midrange, that was always a weak link for me (but do more to my speakers than the CD player), is now more detailed, which I definitely prefer. So, for $1,600 I got a little more bass control, mental satisfaction knowing the soundstage is better, and a definite improvement in the midrange, which I needed because of my speakers (i.e.: you may not). Additionally, I do hear an audible difference on Redbook CDs that are not well recorded. Its not a miracle (in that it wont make really bad CDs sound good), but I can now enjoy more of my collection which is a good thing.
Take this information with the knowledge that the industry indicates that the PS Audio DL-III (i.e.: reviews) competes favorably with much more expensive DACs on the market, and most- if not all of the DACs within its price-range.