Definitely for rack use
I finally dropped a good chunk of money on a bit of studio equipment, and to interface with it all, I bought one of these. At first glance, the FCA1616 seems like the best bang-for-buck (an overplayed saying, but fitting here), and I was specifically drawn to it for the Insert connections built in, but I'll get to those in a minute. Eight channels in and out without even adding another ADAT interface is also a big plus. The system works well in terms of software integration (better on Mac, it seems Core Audio jives with it better than setting up the drivers on Windows), everything works, and the headphone amps are, especially for $250 of kit, absolutely pristine. However, there are two strange issues, one of which took me way too long to figure out.
First, the regular stereo output volume from my Mac was clipping the interface like crazy, but that was easy to fix in Audio MIDI Setup. Nothing too hard, and I could have just done it in my DAW as well.
Second, the four preamped mic inputs sounded... tinny. You had to crank the gain up to above 75% to get a decent volume (I'm talking halfway up the metering in Logic), and they were lacking in bass. The four 1/4" TRS inputs on the back were so quiet they were basically useless. However, sending the outputs of my dedicated mic preamp rack into the INSERTS sounded great. I bought it in the summer of 2014. It's now April 2015, and I JUST figured out the issue. I'm not 100% clear on the circuit flow of the interface, but it seems that the return from the insert of each track is the actual input, so any input signal would have to travel from the plug, through the pre if applicable, and then through the insert jack, and anything plugged into it. The sound I was getting (quiet, but still distorted and noisy from the gain) seems to suggest that my unit's insert jacks are not fully (or properly) normalled, so a bit of signal gets across the connections but most of it is just lost. I'm not going to say this is a dumb or bad move, because this thing is basically intended to be put in a rack, and the smaller, more portable FCA610 lacks inserts altogether, but it is a slightly odd design choice. Alternatively, it could just be an issue with mine, but it works fine set up like pro equipment should be, with each insert split and sent to a normalled patchbay, so I'm not complaining. When it's all connected right, it's the best-sounding $250 I've spent.