We're going to have the same problem you do, since DS6 is midway through 4th grade EPGY and will top out of the OE 7th grade curriculum by 3rd grade at this rate. I do think the instruction in EPGY is better than in ALEKS, and you can't jump around so you get the lecture automatically before each new piece.
We also use Rightstart Math. At DS's (and certainly your DS's) levels, most of the curriculum is too light. However, I think it's really fabulous with geometry. It incorporates a lot of drawing, math-art concepts, and manipulatives to make it fun, too.
