[I3eyond]

Rig in sig.  
 
Which component, amp or DAC, do you think is the weak link in my setup?

 

[DemonicLemming]

With AD700s?  Neither really represent an obstacle.  If I had to upgrade one or the other, though, it would be the DAC - I'd sell the V-DAC and the USB cable, and put the money towards a better multi-input DAC and go optical. 

 

[I3eyond]

Well, I do plan on going HD650 soon, and was wondering with that in mind if I really have any "weak" links that would REALLY be holding me back...
 
Sidenote: My V-DAC can go Optical, both SPDIF and coaxial... Should I be using one of those over USB?

 

[DemonicLemming]

Ah.  With the HD650s, I'd definitely look at swapping the DAC first, and then the amp later on down the road.  Of course, that's assuming you're not going to be perfectly happy with the setup you have now when you plug the HD650 into it.  Things can always be improved, but a lot of the time they don't need to be improved - really your call once you get the headphones.
 
I personally prefer optical, as it gives complete galvanic isolation from my computer, and (probably just my mind) the USB input with my particular DAC sounds a little weedy compared to the optical input.  There really shouldn't be much difference between the three different styles of digital input, though.