I can't address your amp specifically as I have no experience with CJ, but my Quicksilver Mini Mono's can take all the tubes you mention and are auto-biasing. As a broad generalization you can count on getting a bit more UMPH in the low end with KT88's and generally a fuller sound. Going back to EL-34's may be difficult at first as they may sound 'thin' in direct comparison, but can be very musical and detailed at the same time. Which is "better"? That is really up to you. YMMV and your preferences and room and system will have tremendous impact on which works best for your ears. For me, I prefer the KT88's in my Mini-Mono's. If your amp is manual biasing then you obviously you would have to re-bias for the different tube (or for any tube change for that matter). But do check someone who knows your amp to make sure that the circuit is designed to use all those tubes since many amps are not.
Marco
Marco