Its hard to make an assesment based on the info you provided. Your weight and riding ability?
Generally; stock xr600 fork springs are way soft, even for the lightest riders, so if it feels harsh in rocks, my quess is that higher rate springs where installed. To soften this, you can first try 7wt oil at a lower level. (the lower the level of oil the softer it will feel). You should get a manual to find proper oil hieght specs and changing / filling proceedures.
Keep in mind that what works in slow rooted, rocky sections, will have an adverse effect on high speed whoops and g-outs. Good Luck. Feel free to e-mail me. I have set-up more than one of those 6honeys.