When I ran 80/20 dual sport tires on my XL600, I just used hand pressure to set the tires. For the street, I would air them up to the point that I could no longer deform them with my hands, and for the dirt I set them so I could squeeze them about 1 cm. Real scientific, huh? I'm guessing I was in the 23-25 psi range for dirt, and they still felt safe on pavement (no need to air up before heading home).
Have you seen the new Metzler Karroo 3? A bit more aggressive than other DS tires, and might be a good next set for you.