Hi Sarah:
My very first curriculum buy was Sonlight K. My thoughts are that you have quite a while to work on your DH!
I don't understand Sonlight I guess. They have such complicated reading, reading, reading...did I say reading? I know your son is advanced. But IMHO, I think like Carrie! It's best to save the technical stuff and heavy stuff for when children are better able to understand what they are really about. Kids can't process this information as it should be. Why not let him get a basic understanding of his own country to have something to apply World Cultures to first? Couldn' t you add in some world culture material as it relates to HOD topics? That would be cheaper, easier to do as you don't have to find 3 other subjects and pay that horrendous price!
Not bashing sonlight or telling you what to do by any means. But I just feel it's my duty as a neighboring Arizona homeschooler to steer you away from the "other" guy. It just seems it would be easier to add to HOD than to spend $400 when you have to find more subjects to add. I'm sure you could find something your DH would like for $400, now couldn't you? Little bribery never hurt anybody!
Okay, I've done my duty, I'll go back in my corner now.