Alexa - I haven't ever used that pack, so I don't know exactly how the height adjustment works. But, it is common that men and women who are the same height have very different torso lengths. You may need to adjust the pack to be a little shorter (most women have longer legs and shorter torsos) or longer than your husband needs it. You also may have to fiddle with that. The adjustment is probably fine if you can get the shoulder straps flush with your shoulders while the waist belt is secured around the top curve of your hips.
I think I see what might be bugging your neck and upper back. Where is the weight hitting you? Do you feel it in your shoulders or more on your hips? You should feel most of the weight on your hips NOT your back. My guess is that you are carrying a lot of weight on your shoulders, which hurts. The trick to adjusting the pack to distribute the weight is to 1) adjust it loaded (use a kid, or if too wiggly, use flour, water bottles, sand bags, etc. instead) and 2) adjust the straps in a particular order.
First, loosen all of the straps. You need to loosen the main waist belt, shoulder straps, the "load lifter" straps which are the ones on top of the shoulder straps, and the adjustment straps on both sides of the waist belt. Put the pack on with weight in it. Get someone to make sure the kid doesn't fall out in step 2. Bend over carefully or have someone hold up the pack from behind you. It will pull you over backwards with everything loose. Next, fasten the waist belt so it rides on the top curve of your hips or between there and your natural waist and tighten the main waist belt strap. The pack should be secure on your hips and totally falling over backwards if you stand up, so don't.. Then, tighten the shoulder straps under your arms. Pull them as tight as you can comfortably get them, not tighter. Pack should feel heavy, uncomfortable, and secure. Tighten the load-lifter straps on top of the shoulder straps. This should take the weight off your shoulders and make it relatively comfortable. Last, tighten the adjustment straps on the waist belt (two on each side) to snug the back into your back.
It sounds like a lot, but you shouldn't have to do it more than a few times. You won't get the pack to fit both of you if you only adjust the main shoulder straps and waist belt. It will always feel off. The whole process should take less than five minutes the first time and much less time (<<2 minutes) after that.
The ergo is almost certainly easier for daily/routine use, but the Kelty can be useful once you get the adjustment down. Hope this helps!