Never boil pre hopped kits for any amount of time! You loose some of the hop bittering/aroma,& flavor. Not to mention,pre-hopped LME's will start to caramelize at the same time. Def not a good thing! Just don't do it. And a couple pounds of sugar? Who in blazes told you that? Never use more than a pound,since it'll dry out the beer a bit much,& make it seem "thinner" to boot. I like to add 3lbs of plain (un-hopped) DME to a 1.5-1.7kg can of pre-hopped LME. Then of course,you just have to add 1-2 ounces of hops to balance the beer out against the added malt (DME/LME,un-hopped). Oh darn. These basic additions will give a nice beer of 4.8%ABV or so. And won't be darkened by boiling.
Everything works if ya let it-Roady(meatloaf)