Plan to buy RME Fireface 800 - opinions from SONAR/FF800 users ?

I have tried the Fireface 800 for a week-end (rented) and plan to purchase one.
 
Opinions from SONAR users who use (have used) this interface ?  (8.5.3 *and* X1)
 
I have been using ADAT lightpipe Frontier Design Dakota for about 14 years now, and although this still does a great job, I wish to upgrade and have some ''crossover'' solution ''outside'' the PC, still using an external digital mixer (Yamaha 02R).
 
Thanks,
Rob