Or USB to SPDIF if you prefer 
 
I have a Bushmaster 7530 with my blu-ray and AK100 plugged in. I'd like to plug my PC in too, obviously no digital out or USB in on the DAC. I cannot continue to use my blu-ray as a disk reader (not all music on discs), and AK100 clips the end of my purchased mp3s. yay.
I like the style of the Bushmaster, i have just bought some AKG K702's for £160 and would like to buy an Amp soon 
 
 
 
While i've read what head-fi has to offer, i'm still left confused on the whole subject. I've been most impressed with the AK100 --> Bushmaster --> DT990 premiums
It's perhaps not the best i can get? But not too fussed. I fail to understand how some USB to SPDIF converters cost lots, and others not. I had presumed it's all digital and no real processing is going on. Jitter seems a big argument here, is that all it's down to? If so my hearing experience and lower quality headphones shouldn't be of any issue here then?
Ebay has a FanMusic converter for £20 delivered. Legit? 
 
 
 
Also where is everyone buying their stuff from? I've not been lurking here much recently and there doesn't appear to be any actual shops sponsoring Head-Fi. 
 
 
 
Thanks in advance. 

Self bump. Anyone with the answer?

People are not being unfriendly. Unfortunately to give a complete explanation to your queries would be both time consuming and controversial on this forum. So it's unattractive to answer in detail. That's all. You might be able to do some research on your own on the advantage of single step USB > Analogue as opposed to the old style 2 stage raw data > S/PDIF (timing data added) > analogue (voltage generated) method.
 
In brief. Your Beresford and, to a lesser extent, the A&K are now practically obsolete. USB 2.0 is such a more elegant solution hardly anyone puts S/PDIF ins and outs on their products anymore. Running a ~$2000 system through a $20 USB - S/PDIF dongle might work acceptably. Then again it might not. Worth a try if your finances aren't in as good a state as they were when you bought the rest of your gear.
 
Otherwise take my advice. Bite the bullet now and get yourself a good quality USB 2.0 audio interface.