Hi,
 
FWIW...
 
I recently upgraded from older Presonus FP10's to a Focusrite Liquid Saffire 56. I also purchased a Presonus 1818VSL to use as a mobile recording unit. Both of these units have ADAT and I was planning on using that to connect them to allow more inputs. Unfortunately, I have yet to actually connect the 1818VSL to the LS56 - I have tried the word clock connections as well as the ADAT but no workie. I do have a Focusrite ISA 428 pre with ADAT and that works great when connected to the LS56 so I know that the LS56 is working via the ADAT connections.
 
I did connect the 1818VSL by itself using USB with my system and it seems to work fine, however, I prefer the LS56 liquid pres since you can get quite a variety of "virtual" combinations. I also connected the 1818VSL to my Gateway i3 laptop which is my mobile system - I just can't get the 1818VSL talking with the LS56.
 
The only downside of the LS56 is the monitor software is a bit daunting until you get your head wrapped around it. Once you get over that, I find it very usable. Also, it does not have the compression/reverb built in like the 1818VSL software, I can patch that into the LS56 via outboard gear.
 
My Focusrite stuff has been very stable and the LS56 sounds great, however, it is a bit out of the 1818VSL price range at $999, but after using it, I really like the LS56 and it is proving very stable on my system (I recently upgraded to a ASUS/Intel i7 32GB Windows 7 64bit PC too).
 
Take care,
 
gs

@gibsongs

What round trip latency do you get from the 1818VSL while running soft synt ? 

The main reason of my upgrade for more channel is to record my woodwind/brass band (with drums and rhythm section) from time to time (audio recording).

For soft synt, I use Garritan Jazz Band to do arrangement for this group.

While, I'm happy with my current Quad Capture for soft synt, I need to increase the Quad's buffer to 96 or 128 samples if the soft synt tracks (Garittan) grows to around 10 and above.

For my Quad Capture / @44100
128 samples - 12.1 msec round trip
96 samples - 9.8 msec round trip
64 samples - 7.6 msec round trip

I am hoping one interface does it all - good or better round trip than the Quad Capture, as well as more channel.

Thanks.