Hi Rob,

You will gain the following additional features for the relatively small additional investment:

- Dual reference class Parallel Conversion AD converters per 4 x mic preamp/DI
- reference quality preamp technology based on the Micstacy
- USB & advanced Firewire Connectivity vs Firewire only with the FF800
- integrated EQ, Dynamics and Reverb/Echo effects in TotalMix FX
- 30 Input/30 Output channels vs 28/28 in the FF800
- 2 x MIDI I/O vs 1 x MIDI I/O with the FF800
- 12 Analog I/O vs 10 I/O with the FF800
- 2 x Stereo headphone out vs 1 on the FF800
- XLR Mains Output on UFX
- Wired Remote control with Optional Hardware Remote Control
- AES/EBU I/O
- a high-resolution color display
- advanced stand-alone operation with integrated digital Monitor Controller
- front Panel USB port for future addition of recording/playback capability

Remember also that the Fireface 800 is considered by many to be the "best interface in class" and can support simultaneous use of up to 3 Fireface 800's at once, a feature not available with the UFX.

Compare what features you need now and in the future to the differences between the 800 and UFX to determine which will serve you best. Also realize that the 800 is considered by many to be "best in class" and the UFX shares a number of technologies and builds on some others:-)

Thanks Blair and Knut. 

Just trying to figure out what the M-Series (Micstacy ?)  would really make up a notable difference (when compared to FF800).  While other features may be of interest, I don't see (yet) the use of these (please keep in mind I am moving up from a very basic PCI card (Frontier's Dakota) to something in the high end - FF800 represent a huge move I guess. To be frank, I still have to figure out how I will now blend such an interface with an external console (Yamaha 02Rv2 - certainly much less preamp quality in its era), learning to play with the Total Mix all along with Sonar mixer and physical mixer.... 

Not sure I'd make use of DSP effects of the UFX immediately... Not sure having a 2 inches monitor at my knees level in a rackmount will be very useful... or replace my dual-monitor setting on PC ;-) 

So for the immediate, I guess my very main question would be about real (audible, concrete) difference in conversion AD/DA between FF 800 and UFX... That'd be the *now* that could make me go for the extra bucks, and I agree with Blair that I may have eveolving needs (or the day my 02R drop me, I can still fly, and probably fly higher - although then I don't see the use of dual ADAT on either units !!...) 

One last question: I read about ''available digital outputs'' that may vary depending on using less or up to 192Hz: does this mean that I would then need to stick lower than this if I need to keep my 2 x (8x8) ADAT - 16 channels working? (And if so, would the *upper-quality* of the conversion of the UFX compared to FF800 just be lost ?)

Sorry if my questions may sound very basic, these are the concerns I have in my purchase decision (I *will* purchase one of these two for sure), and nothing above means to be sarcastic.

Thank you very much for helping,
Rob