Danny Danzi
Sharke, here's how I do my stuff. It doesn't totally address your problem, but it works for me.
 
I use a master bus in each project. That bus is set to my main soundcard outs 1/2 during an export.
 
I create 2-3 buses that have an instance of ARC with the speaker correction I need.
 
My master bus outs during mixing will be sent to the ARC correction of my choice so I can hear the right monitors in an instant.
 
This comes up as a template for me. Before I saved it as a template, I ran test tones through the ARC buses with each different correction going on. Instead of messing with the trim on ARC, I adjusted the bus ARC was on in Sonar. I'm not sure how accurate that meter in the plug is and to be honest, I really don't care as I never look at it or even open the plug. What I do watch is my Sonar bus meters and make sure there is no clipping or weird sounds going on. 
 
When I'm read to export, I just set my master bus out to my main soundcard 1/2 and never worry about ARC. I usually play an entire pass of a mix through my master bus without ARC just to see what my final output levels are. I'm usually a little under -3 dB so I'm in good shape.
 
The test tone noise I used was inside my PSP Xenon limiter. It has some handy metering and tools in it so I used them to see how things were looking.
 
So to answer your question....
 
"Does this mean that as long as I have the trim control set to unity, I shouldn't worry about the effect that ARC2 has on levels when I'm mixing? In other words, when I eventually turn ARC2 off for the export, the levels I've arrived at with ARC2 on will still be correct?"
 
In my experience, I have NEVER gotten the same levels with ARC on or off. They are always different even at unity.
 
I pay no attention to the ARC trim and adjust the bus ARC is on. That's what I set using the Xenon test tones. This way I don't ever open ARC. The same is true with ARC 1 for me...which is my preferred weapon of choice over ARC 2. Hope some of this helps.
 
-Danny

This is pretty much what I've been doing (except for the test tones), although you're right I shouldn't touch the ARC trim just adjust the bus level like you say. I haven't done any exporting since I've had ARC and I know I'm going to forget the first time and export with it on lol......and I wish I had multiple sets of monitors to set up 3 ARC's with! 

Danny, quick question:  why ARC 1 over 2?  I am still on ARC 1 as well, but was considering an eventual upgrade.  Any insights as to why you haven't made the switch?
 

if you route all of your sub busses (except ARC) back to MASTER....
 
(normally, master would be routed to the sound card)....
 
and THEN route the master to the ARC bus with arc on it, 
then you can STILL track your peak levels on the master, as it should normally be monitored, 
and bring the arc down to match the master.
 
 
some folks have been confused about the gain staging...
make everything in arc happen DOWNSTREAM of the MASTER BUS.
 
 
then, when you do your actual output, simply turn ARC off, and re-route the MASTER back to the soundcard.
 
i even route the ARC bus to NONE, once i'm finished with it.
 
 

sven450
Danny, quick question:  why ARC 1 over 2?  I am still on ARC 1 as well, but was considering an eventual upgrade.  Any insights as to why you haven't made the switch?
 

For some odd reason Sven, ARC 2 made the sound in my room a bit more high endy. If I trusted it, I'd wind up pulling the high end out of my mixes a bit more. It's not super bad...but bad enough to where my mixes were sounding a bit dull and missing that nice high end. I tried to use the eq in ARC 2 to manually bring the top end it's adding down a bit, but there's still a bit of sizzle going on that I don't like that ISN'T audible when using ARC 1.
 
As you can see, there is a peak all the way to the right on ARC 2 that was corrected on ARC 1. I adjusted that manually so the peak was gone but I still hear a little something that I'm not down with. If something isn't broke, I don't try to fix it and ARC 1 does what I need it to do. There isn't much difference between the two when listening to projects...but I hear this little extra sizzle in cymbals and especially guitars that I KNOW isn't being mixed in on my end. Highs are something I've never had a problem with so I didn't want to start messing around with that stuff.
 

Hey, if it ain't broke, right?  Thx for the reply Danny.  Maybe that's a bit of dough I can now aimlessly throw at something else....