Xonar Essence STX with Beyerdynamic DT880 (600 ohm) - Whats next? opamps? amp?

I currently run a Xonar Essence STX with some dt880/600's via the headphone out.  I feel the upgrade itch and am ready to make my next move.

I have been drooling over a Woo Audio 3 for quite some time, and am considering it. 

However, I realized I have yet to dink around with the opamps on my card.  Are they worth it??

I have searched on this, but most of the threads go into way to much detail with regard to the opamps, and I get lost.  So my question is - does which opamps I pick have to do with the cans I am driving?  Do those considerations change if I decide to use line-out to the woo audio 3 then to my beyers?  I know there are 3 opamps on the card to be swapped, and only 2 of them need to be touched if you intend on only using lineout.  Essentially - are opamps matched to the cans, or are they just inherent to the card and its really irrelevant to the attached cans?

Is the WA3 worth getting (for me)?  Again, I have searched on this, and I know for sure that the WA3 and the dt880/600's are a match made in heaven, but, will my whole system be severely handicapped with stx via line-outs as my source?  I'd like to notice a difference if I am to spend 500 usd. :)