Miss T., I understand your concern. As moms, it freaks us out when our kids won't eat like we think they should, but from your post, it sounds like the 6 mo. old is healthy and growing, so I think he's getting enough to eat. Now whether he's getting the right nutrients or not, I can't say. But my daughter hated baby food. I bought maybe 20 jars before it became crystal clear I was wasting my money. She just wasn't interested, and after tasting some of the baby food myself, I couldn't blame her! Until she started teething, I simply put mixed cereal in her formula bottle and gave her easily gummed items like sweet potato veggie puffs (I can't recall the brand name, but they're marketed for little ones and practically dissolve on the tongue). I do not recommend giving him any fruit juices, not even diluted with water, since you'll end up with 'Star Trek' poop in the ol' diaper (he'll poop like no other baby has pooped before !) plus fruity smelling poop is just awful. Uggh!
Anyway, I hope this helps. But as long as your doctor doesn't feel it's a problem, don't sweat it and supplement his formula with cereal. Then when he can chew solids, start giving him the good stuff - real food!