The whole IFS is whats limiting your travel. I think you would need longer front control arms,long travel struts of some kind. I also don't know how much the rack and pinion is limiting it? I think getting rid of the rear swaybar and putting "disco's" swaybar disconnects up front will give you a bit more travel too...
Double stacking is kinda Ghetto IMO. They used to do that in the old days with blocks in the rear,and was totally illegal in the state of NJ. If you don't get better coils up front you'll feel very wobbly side to side. I noticed it with my RC Spacers up front .
Solid axle swap will probably cost a couple thousand to do it right. You might need a different t-case if you cant get the driveshaft on the same side as the front axle. Then a new steering box and all new steering components,then to get the geometry correct so you don't have any death wobble like Cherokees get..
If I was going bigger I would do the 4"or4.5 from Rusty's offroad,a set of 33s and just pick better lines when your wheelin. My 01 Cherokee with a 3.5" Rubicon Express lift,trimmed fenders and 33 BFG KM2's it handles all the blue,green and a couple of black trails in Rouch Creek. Then again it was a solid axle coil sprung vehicle !!