If you want to cut large box joints in the ends of stock you can stand in your tenon jig, there's a relatively easy way to do that. (Not as easy as the I-box.)
Just choose the width of finger you want, and rip and plane shim stock to that thickness. Set your dado stack to that thickness, and adjust it to cut the outside edge of the stock. Put a pile of shims outside that and clamp. Now you can make a cut, move two shims to the other side, retighten and recut. Repeat until all of the parts have fingers cut on one end. For the second side, start with one shim on the inside and the rest on the outside, and repeat the process to make matching joints.
It has been a while since I've done this, but it worked beautifully for joining 2x4 stock to make a solid small lathe stand.
Just choose the width of finger you want, and rip and plane shim stock to that thickness. Set your dado stack to that thickness, and adjust it to cut the outside edge of the stock. Put a pile of shims outside that and clamp. Now you can make a cut, move two shims to the other side, retighten and recut. Repeat until all of the parts have fingers cut on one end. For the second side, start with one shim on the inside and the rest on the outside, and repeat the process to make matching joints.
It has been a while since I've done this, but it worked beautifully for joining 2x4 stock to make a solid small lathe stand.
You'll need to rig up a support to clamp the stock vertical, but then you can cut the notches to the max depth possible with the IBOX. Then use a handsaw and chisel (or other means) to extend the depth of the cut.