What about having him learn a second language? I know there are many parents on the board here who use that as enrichment or have it already as part of their school's gifted program.
Do lots of hands on things that aren't just books. Like if he were interested in bridges, he could read some books and then design and build his own bridge with balsa wood, lego bricks, or whatever material you had. Let him help you cook (safely, of course!) to do fractions.
I agree with DianaG, our son's school did Reading Eggs. It got repetitive and for gifted kids, it's like nails on a chalk board to have to keep repeating tasks.
My son likes to watch Maths Mansion off Youtube. IXL drives him insane, mainly because if you type in the wrong answer, it subtracts from your score far more than it adds to it for correct ones and a finger slip on the keyboard causes a lot of frustration in that regard!
There are programs you could do at home that homeschoolers use. I've never used it, but many friends have used Time4Learning and liked it. It's $20 a month. When I homeschooled last year, I used Alpha Omega's 4th grade curriculum. I think it would be available on sale somewhere like Amazon for about $100 per grade level per subject, but I paid about $400 for a full 4th grade curriculum.
