the converters on the H-8000FW are very good. Admittedly they're not PrismSound, DAD or Lavry but they are very good. At least this is my personal opinion. I have a similar situation where I felt that I am not doing justice to my H-8000FW by routing its outputs into an RME Fireface 800, so top quality converters are definitely on my list although I shiver at the idea of how much would I have to pay to have all my synthesizers connected this way.
Maybe the guys here at Eventide can tell you more about this issue.