tried many methods, here're my results, hope this helps...
going from gb 2.3.3 rooted with cf root ...to 2.3.6 with cf root.
(all firmware from "check fus 2.1")
uk(02)...JQ8 -not easy!
eventual success, method mentioned in last page of link
Poland play... JQ9 -easy!!
used pc version 'odin3 v1.7' to flash firmware, then again to flash 'cf root kernel' (same one as in the above 'xda' link).
result -all good
tried using mobile odin pro first but had probs.
if all else fails, you could try, team overcome's custom rom, i tried that too but didn't like their version of cwm, so was determined to get chainfire's original working.