Wish I had the time/money to get all three and compare. They're all so good, it's mostly what features you prefer.
That said, I'm totally happy & in love with my FF800. I'll never give it up, and I wouldn't mind having a few more. (The Orpheus has me tempted, though....) For what I do - often under 10 mic inputs, it's more than enough, and the matrix output feeds everything; monitor speakers, headphones, SP-DIF backup recorders, you name it.
For external pre's - I have the Grace M802, w/8 channels, I route directly from the Grace DB-50 output into the FF800 with a 6" short breakout cable, into the eight TRS 1/4" jacks in the back of the FF800. With the two mic pre's on channels 9 & 10, I now have a 10-channel HQ recording system that will interface with my laptop running Samp/Sequoia. The FF800 mic pre's are very good on their own, but I often save those two inputs for final, last-ditch inputs; sometimes just house/ambient mics, etc.
I could have gotten an AES-EBU interface from Grace, which would have kept the A/D conversion inside the box, but would have had to send it to them for the install, and it was very very pricey; more $$ than the FF800, with none of the input/output & routing matrix features. Glad I didn't go that route. 6" of modified cable doesn't seem to make much of a change in the sound; the FF800 converters are rock solid, and sound great. ;-)