What are the main differences between dedicated studio monitors and ordinary speakers?

Being able to calibrate the frequenciens to some extent is an important feature in tuning the monitors for DAW use, but the ability to do so does not mean the loudspeakers are any good soundwise.

I could not find the slightest bit of information on Goodmans 75s in the internet, but the one picture I found gave me a very "light weight" impression. Anyways, without knowing any specs or anything, I can't say how the Behringers compare to those Goodmans. The Truths are usually considered as monitors of quite a good value to money, though.

Most of the home audio gear is designed to give a "colored" sound.....one way or the other. Most augment the bass freqs in some way to enhance the sound. 

You want to mix with speakers that are flat across the spectrum. As has been pointed out, that is not always the case even with studio reference speakers. The room you mix in plays a major role in what you hear as do the speakers. Start with good reference speakers. Then work on the room acoustics. 

I use ARC. (Acoustic room correction software) 

It's OK to use home speakers to check the mix after you mix it properly with flat response monitors in a controlled room.  

note: My Mackies have frequency controls on them. This is so that I can adjust the freqs as I tune them to the room using hardware or software for that purpose.  Truth be told.... I set them to where they sound good and never adjust them again. Then I learn the speakers and the room....and mix with that starting point. 

i own a pair of behringers (8" woofers, 2031A i think) and they are a good place to start vs home audio speakers. i would encourage you to get the 8" ones for some slightly better bass response. you would probably do just fine with the MAudios too, but i can't vouch for them and you won't get the bass response that you would with the behringers (particularly the 8" ones).

to speak on monitoring in general, a lot has to do with your environment and far more how you "learn" your monitors. by getting a pair of studio monitors, you are heading in the right direction since they are all designed to reproduce the details of sound vs. pleasant sounding music. frequency response flatness is only one part of the equation, the other is responsiveness of the speakers which determines how finely the details are reproduced. however, all that is for naught unless you train yourself to listen for these details and make a connection between what sounds good on a well-mixed/mastered album and your own mixes.

i've spent years mixing (even with the behringers) and while i've gotten better, i can still quickly embarrass myself by playing my mixdowns in a car stereo. part of this is my mixing environments haven't really been that conducive to picking up the subtleties of low end frequencies, but most of it is that i don't have the experience (and probably, talent) to translate what to me sound like pretty subtle differences on the monitors and pretty big ones on my stereo.

i say all that so you will have the proper expectations and not be disappointed that your mixes don't sound "good" - they will probably get a lot better, but they most likely won't stand up to a commercial mix until you keep at it for awhile. comparing your mixes to commercial ones is the best way to learn, as well as listening on different consumer systems (home stereo, earbuds, car stereo, computer speakers, etc.). the important thing to do when comparing is realize that louder sounds better, so you need to turn the commercial mix down so it is at a similar level to your own mix (or turn yours up). 

good luck with your monitor purchase - and this is a great place to come for advice. a lot of pros hang out here (i'm not one of them, i'm just good at learning and writing, vs. actually doing ) and can tell you even more about the fine art of studio monitoring.