Ok, a couple of issues I noticed... You didn't say what size of batch - but I am guessing that you are doing a 5 gallon batch. I am also assuming that you are doing an "extract with grain" recipe - and not a mini-mash. OK, that being said....
13 pounds is a heck of a lot of malt extract for a 5 gallon batch (but might be applicable to the style - I don't have BeerSmith here at work to run the numbers). To say that you want to try to "bring [the FG] down lower" by adding brown sugar is incorrect. To say that you want to replace some of the 13 pounds of extract with some amount of brown sugar is more accurate. You will be replacing some of the maltose with sucrose - and you FG will be lower than if you just used the 13 pounds. If you add the brown sugar to the 13 - it will be higher, naturally. That should work fine as long as your simple sugars do not add up to more that 15-20% of your total fermentables - otherwise you will get a "cidery" taste.
Secondly... The Pope says that if you are going to do an "extract with grains" brew - then you should always use the palest malt extract you can find. Get your flavor and color from the steeping grains. Leave the darker colored extracts to the "extract only brewers", like Bub, so he can make his table sugar brew and film himself chugging bottles of corona on YouTube.
Thirdly, nix the 2-row - unless you are doing mini-mash. That grain needs to be mashed at a lower water/grist ratio at a specific temp in order to convert and is not applicable for "extract with grains".
And finally (and probably most importantly) - in order to dry it out a little more - get yourself a fresh, well attenuating yeast, make a starter, and aerate before you pitch. You will need a decent amount of healthy yeast to make it through all the sugars in that big beer. Go to
www.mrmalty.com for the yeast pitch rate calculator.
Good luck my brotha! Brew Strong!
Mylo