The LED labeled "LKD" that I mentioned earlier tells you when the unit is "Locked" to it's internal sync clock or locked to an external clock.

The installer should be run BEFORE connecting the device to the computer.

On a Windows system it will use ASIO drivers. On a Mac it will use Core Audio drivers.

You can use up to 8 channels when using ADAT but this drops to 4 channels when using 88.1khz and 96khz sample rate settings.

The unit will likely need a firmware update when first installed.

Now things are getting interesting. The mixer software is a LOT nicer than my old Echo's software mixer. Tons of control and doohickeys. This part is cool. You can make 6 separate monitor mixes that don't affect the DAW in any way. That way you can have a mix for the engineer and others for the artist(s). So if the artist wants to have certain things turned up or down in their headphones while tracking that can be done while the engineer can monitor things how he wants without having to fiddle with stuff in the DAW or use external hardware (like a headphone mixer). The Focusrite mixer handles it. Also you could have different monitor mixes for various tasks ready to go just by clicking a tab. Not sure how this would be routed yet or how many of these mixes can be playing at once but definitely useful. I'm guessing you would maybe use the main outs as TRS stereo sends (that'd be to separate mixes), the two SPDIF (two more stereo mixes), the headphone jack (one stereo mix) or maybe do it through the optical connection. Perhaps this is common with newer interfaces but I don't think my Layla did this stuff so to me it's pretty nifty.
EDIT: My mistake. You can have six MONO mixes or three STEREO mixes.

When using a 1/4" cable through the multi in connectors it seems you have to set the inputs to either "line" or "instrument" on the Focusrite mixer console depending on what you were doing. I think my Layla did that automatically but I don't remember ever trying to use those multi ins for line level stuff so I don't know.

I find this a little odd. There doesn't seem to be a way to adjust input levels within the mixer. It has to be done with the knobs on the box, external hardware or with the DAW. The fader only affects the monitor level. I'm guessing this is true of the pan fader as well.

So the routing section is very nice. You'll have to look at the manual yourselves for more detail but everything is right there and easily accessible. With the Layla it was quite confusing and you had to cycle through various screens on the mixer to get at stuff. With this all you have to do is click on what you want to change and select from a dropdown. You can also name your inputs and outputs through various methods. There are three routing presets. "Clear" which just resets everything on the mixer. "DAW Tracking" which sends the DAW outputs directly to the outputs on the 18i6. It says when using this you have to monitor the inputs being recorded into the DAW directly from the DAW. I'm not sure what that means but I assume it's a latency thing. "Zero Latency Tracking" which sends the output from the DAW to one of the monitor mixes instead of directly to the outputs. Tracks being recorded would then be monitored through the Focusrite mixer instead of the DAW or you get the same signal outputted twice. So yeah... that's confusing me a little but I'll figure it out.

The monitor control section of the mixer has a whole pile of wacky options for what is and isn't controlled by the big GUI level knob. Tons of stuff I couldn't ever see myself using and I won't try to explain it all but even with all those options it seems very simple to use. At first glance it looks like it only applies to the headphones and main outputs. Again it is all right there on the main screen without having to flip through tabs or menus. It probably changes for each of the mixes that have been created but I can't tell yet from the manual. Someone certainly put a lot of thought into it. Very nice. It says that these settings are independent of the physical monitor/headphone level knobs on the front of the unit so I think this means you'd set the GUI monitor levels and then you can adjust them further with the front panel knobs. I'll mostly be using the front panel knobs to control the headphone and monitor levels.