DewtimeMusic, first a caveat: I have a SX90R alto (black&gold) that I will be selling, but have just been too lackadaisical to post yet. Hopefully those used to my posts can confirm that I'm relatively (gotta give myself some wiggle room) objective in cases like this when I post an opinion. That is, even though I have a terrific, almost virgin JK I could sell you, my following comments are as objective and ethical as I can make them and are not intended to influence you towards any given purchase. However, if you are interested in discussing my horn, PM me.
I have played the Cannonball and have owned both the lacquered and black&gold-finished JK SX90R altos. For me the Cannonball had an individual sound to it, one that I didn't care for. It had power and presence but the core sound just seemed to me to have a bit of a tinny quality. In all fairness, I did not spend a lot of time looking for another mpc to match it with in order to see if I could get a more substantial sound out of it. The mpc I used was a Ponzol HR. Otherwise, the horn was responsive and with good intonation.
The JK, OTOH, has a more substantial sound. IMO the black&gold has a more substantial, if not a bit darker, core sound to it than the Cannonball and, perhaps even than the lacquered JK. (My tenor is also a JK b&g, so I must have an affinity to that sound.) I think that with another mpc, this horn could come up to the brightness the OP is seeking. I don't usually seek brightness in my sax sounds, so I won't exhibit that unless I intentionally counteract my equipment and/or attitude when I play. I have no doubt that if the JK were matched up with a mpc that is brighter, like my Ponzol SS alto, or more smaller chamber and/or high-baffle mpcs, what you would have is not just a brighter sound but (and this is important to me) a brighter sound built up from a more substantial and deeper core sound than from many other saxes' sounds.