I think it partly depends on what 6 inch lift you have. If the lift has a spacer already then you wouldn't want to add another spacer.
I have a 6 inch stage 1 pro comp and a body lift right now as well. I was also looking into how to add more lift and I was told that the best way would be a new set of coilovers like the radflo 2.5, PRG UCA's, and a Deaver Leaf pack. This would give about 2-3 more inches of lift and can all be purchased from greg at PRG. If I remember correctly the pirce is something like $2000.
I have a 6 inch stage 1 pro comp and a body lift right now as well. I was also looking into how to add more lift and I was told that the best way would be a new set of coilovers like the radflo 2.5, PRG UCA's, and a Deaver Leaf pack. This would give about 2-3 more inches of lift and can all be purchased from greg at PRG. If I remember correctly the pirce is something like $2000.