with your budget (£600 was it?) wouldn't consider any less than the DACMAGIC, although the beresford does offer great value.
it sounds better and has more features (especially ins & outs) than the (admittedly bargain) beresford, also it looks nicer and is clearly of better build quality. On the downside Cambridge Audio has recently increased prices so the DACMAGIC goes from £200 to £230, making the beresford even better value (for now?), also the DACMAGIC has no headphone socket (although that won't matter to most because most amps do).
although I haven't heard the v-dac it is priced in the middle, looks cheaper than the beresford and seems well under-specified in the face of the competition (not enough ins and outs)
There are three main ways to get the digital sound from your PC to your DAC - Optical (TOSLINK), Coaxial (SPDIF) or USB, check your computer to see what your soundcard has, from an audiophile standpoint USB is considered less desirable than coax or optical because it's limited to 16bit / 48khz audio, the beresford TC7520 is claimed to be very good if you do use USB (thanks to a dedicated USB upsampling circuit), Coaxial is said to give a slightly better sound unless you intend to use a long length of cable, in which case you want Optical.
The digital ouputs sometimes need turning on in soundcard settings, your soundcard hopefully should have sample settings for the digital connections too, theoretically for the best possible sound quality at this money you should aim for a shortish Coaxial cable with soundcard settings of 24bit / 98khz which the DACMAGIC upsamples to 24bit / 192khz. Maybe worth noting though that since your music collection is likely sourced from standard 16bit /44.1khz CD-quality files and will end up being upsampled by the DAC at 24 bit 192khz anyway, your results with USB may not vary that much - it may all sound very nice.
Plenty of amps to choose from in the budget price range, some recent well-respected offerings from Marantz, Cambridge audio, Rotel, NAD, Rega etc. To be honest the amp should represent a harder choice than the DAC, just remember to save some for cables.