In a nutshell RKII has slightly better cleans, and trust me when i say only slightly better, most people wouldnt notice unless you are fanatic about your clean sound. personaly i like a dirtier clean sound anyway.
The RK II also had the Britt mode worked over, basically more gain and slightly different tone. But i can get **** close with my RKI with a booster pedal in front with gain and drive maxed and honestly I think it sounds better!
Other differences, RKII has two series loops, where RKI has one series and one parallel, second version of RKII has a tuner out where RKI and RKIIV1 had a trigger out.
