I don't understand this at all. 
 
My project uses a Sontius EQ effect on the master bus which introduces a standard V pattern. raising low and high end and lowering midrange. For unrelated purposes, I need to export the audio of this project into Adobe Audition. This last time, I wasn't liking the mix, so I added an EQ filter to the exported .wav in Audition, which was also a standard V pattern. It suddenly sounded much more to my liking.
 
My assumption here is that these two EQ filters are additive. For example, if I raise 500Hz by 3dB in one and 2dB in the other, it would be the same as if I raised it 5dB in just one of them and didn't use the other at all. With this assumption in mind, I decided to "add" the settings of the Audition EQ into the Sonar effect, so I wouldn't need to be using both, and also so I would have this sound I liked in Sonar while working on the project. 
 
So, that's what I did. HOWEVER, it didn't work. (I'm using just the one frequency example here for simplicity, but I did this on the whole spectrum.) Adding 3dB to a frequency in Sonar and 2dB in Audition does NOT sound the same as just adding 5dB to it in Sonar alone. Why is that?
 
Semi-facetious postscript: Also, could someone else just do this for me? I sort of don't like messing around with the mix, and I never feel like I'm doing the projects justice. I wish I could just hand the whole enchilada off to someone. For free.

Of couse  every EQ is different, always been that way. 
Seems odd to just add a random curve like that?? That was common in the 70's as sort of an old wives tale thing poeple did to PA systems and home stereos. I think it was because the speakers used to suck.  If all your tracks are recorded properly and you using good VST's why is your midrange an issue? It's usually the low end that needs a cut in my world. 

(Side thought: you know what would be cool.... A browser plug-in one could install that can automatically play audio when you hover over a hyperlink. People on this forum could then say "I mean something like this" and include an audio snippet attached to a hyperlink, and the reader, who has the plug-in installed, would just have to hover their mouse over it and that would start playing. Maybe there's already something like that.)
 
I don't know, but all I know is that I like it better after I've added that V to it. But my question applies regardless of what EQing I'm interested in. Shouldn't the two effects be additive? Why can't I sum them up into a single effect?

jkoseattle
(Side thought: you know what would be cool.... A browser plug-in one could install that can automatically play audio when you hover over a hyperlink. People on this forum could then say "I mean something like this" and include an audio snippet attached to a hyperlink, and the reader, who has the plug-in installed, would just have to hover their mouse over it and that would start playing. Maybe there's already something like that.)

yes, already there without plugin, it's called javascript (or jquery or webapi etc), and it's how the soundcloud et al player widgets work

You are correct to assume that two EQs in series are additive. A boost or dip of X dB on one should yield the same results on another - assuming all variables are exactly the same, and the plugin isn't intentionally adding harmonic distortion (AKA "tube warmth", "saturation", "color", "character").
 
The big gotcha here is the challenge of making sure all variables are exactly the same. This will be especially difficult in your case, because the two equalizers in question do not handle bandwidth in the same manner. The Sonitus is constant-Q and Audition's is proportional-Q.
 
Many prefer proportional-Q filters because they believe they're easier to dial in. But they do make it nearly impossible to set up one EQ exactly the same as another.
 
 

As bit said, too many variables. If all was were 100% interchangeable it would make most redundant. The closest thing you will get to what you are seeking is to use a match eq like equivocate or melda mautodynamic eq.

different EQ slopes are probably first on my list of reasons, after the distortion and what not that many soft plugs can add, as Bit said.

Cactus Music
Of couse  every EQ is different, always been that way. 
Seems odd to just add a random curve like that?? That was common in the 70's as sort of an old wives tale thing poeple did to PA systems and home stereos. I think it was because the speakers used to suck.

In the 80s and 90s in the UK one explanation was “that’s what producers and DJs do on their equipment so that’s how you make the music sound the way it should”. Or, looked at another way, how you make the vocals and most melodic information disappear.

Something to watch about boosting bass and treble and cutting lots of mid is that while making the eq change our brains tend to think the more mid you cut the better things sound. But going back later and listening with fresh ears the end result usually doesn't have the same impact and is very tiring to listen to.

I don’t know why this happens, but it’s common enough for Mesa Boogie to warn their Mark Series amp users against making excessive mid cuts in the graphic eq.

tlw
Something to watch about boosting bass and treble and cutting lots of mid is that while making the eq change our brains tend to think the more mid you cut the better things sound. But going back later and listening with fresh ears the end result usually doesn't have the same impact and is very tiring to listen to.

I don’t know why this happens, but it’s common enough for Mesa Boogie to warn their Mark Series amp users against making excessive mid cuts in the graphic eq.

Yeah, so I've discovered, exactly as you described. So it's back to the drawing board. i'm Mix Recalling and then removing all EQ from everything and starting over. 
 
Thanks everyone for the understanding on EQ. question answered!