Does that mean it's better to have 2x4 than a single 8?
Also, I remember way back when I did hardware support that we always had balanced RAM, meaning if there were multiple sticks they were all the same. Is that still true and I should pull the 2GB when I install the 8GB, or can I put both of them in?
The lack of optimum dual-channelness is not as big a deal as the the system being RAM constrained. You'll see a big improvement with the 8GB stick added.
Some of the recent "business" laptops from Dell have only had a single memory socket. Lack of dual-channel is not a huge deal in most cases.