Here is a bit of a non-technical explanation, which I hope makes sence.
Studio monitors are designed to be flat - in other words, designed to give an accurate representation of recorded material, so that, if you get something to sound good on a set of monitors, it should, in theory, sound good on everything else as well.
Of cause, there are a lot of factors that come into play. 2 key factors are you listening environment and the kind / type of monitors you use.
The preferred, and logical, way is to have a direct path from console / DAW outputs to a monitor amp, or to bi-amped monitors. There are many reasons for this, one of them being like Gidge said, you'll add another piece of noisy gear, but the main reason is often overlooked.
An example relating to your proposed set-up:
You have used your graphic EQ to make your monitors sound as good as possible. In order to do so, you have cutlow and high midrange frequencies, boosted the low end, and boosted the very high end [very feasible - if you use older JBL's]. Now you start working on making one track sound good, and you apply some EQ on your console. This particular track needs some boost in the high-mids, so you boost the high-mids. The only problem is ..... you have made a cut in the high-mids on your graphic, so you'll find your console's EQ does not work all that well, you have to turn the know all the way to the right to hear any boost. By doing so, you'll add a huge amount of noise.
Now think of that, 2 different types of EQ working against each other, over multiple channels, and you will have created a big problem for yourself.
I'd suggest you use your monitors straight, mix a track, put it on CD or tape and play it on a lot of different systems. See what it sounds like. Use your ears and make adjustments if and where neccissary. There are hundreds of top engineers who use crappy monitors as a standard and produce brilliant work - because they know what their monitors sound like
If you are not happy with the results, look at some acoustic treatment for your working space, and save up for some better monitors.
Good ,luck!