Voltages…

Only tried it with the 5.25V 2A Modmypi PSU so far

powered up pi (bare) = 5.42V
plus sd card = 5.20V
plus hiface 2 = 5.06V
plus ethernet = 5.03V
playing music whilst reloading database = 5.01V

Yes, all working fine at the moment.

Having put the files on a USB drive they played perfectly so I'm blaming the network/NAS for the audio glitches on high bitrate audio (probably the NAS as it has a slow processor and slow drives). I presume that Gnome on the PC does some buffering to accommodate irregularities in streaming from the NAS and the Raspyfi doesn't and hence is more affected by them.

Not sure how I solve that without spending lots of money.

Whatever, with the exception of the few tracks that I downloaded to try the high definition audio, all my music is < 1500kb/s so I'm just going to leave well alone and enjoy the music.