Just a couple thoughts...

1. does the private school offer scholarships, many do:-)
2. would the gifted program at your school really solve most of your problems? (maybe you are not missing much!)
3. maybe you can make contact with local homeschooling group/s and figure out how your DS might fit in, maybe that would might help your DH get his head around it.
4. is online school an option from your school district? (not sure if this is an improvement or not but worth investigating... no stone unturned!)

Best of luck.