Whats the diode in the circuit for? If you are supplying the unit with DC, I can only "assume" its for protection. In which case, its not really needed unless something goes wrong with the PSU and it outputs AC.
*** purely educated speculation as I don't have a unit to look at or the diagram


With respect to the input voltage to the reg being 14.5v and not 15v, I wouldn't worry about that at all! So long as the Murata can supply the required 12v constantly and cleanly (the cleaner the better!) all will be fine. I intend to fairly soon take a look at one of these dacs as I'm really interested to see what I can do with it. Given the rocky start that Stan and I got off to, I'm hoping that he doesn't mind me taking a look and making my own suggestions here in the open!