Im a little confused here... You stated that youd really like to try a urethane ball like the karma or avalanche urethanes, but then u listed that you already have a karma urethane...
Did i mis something, or are you just looking for another one?
Anyways, i dont know your game or what conditions you bowl on. But to me, it looks like your arsenal is complete from the bottom end thru the upper mid range side of things, but if i were you, i would more than likely look at the upper end of the spectrum in order to complete the arsenal by going with a strong solid reactive asymetrical ball maybe even two, one with surface (800-1000) grit to start the block with to help blend out the pattern and then maybe one with a weaker layout and less surface.... (sorry i just remembered you have a Nexxxus in your bag, which very well be just like what i was referring too).
Two balls that come to mind are the Mastermind with a control/midlane layout and OOB surface, and the other would be the Reax Version 2 with a higher angle ratio and slightly higher sum, an a pin to PAP distance that would help retain its energy for the backend once you start plaquing tens...
Like i said.... This is just a complete shot in the dark as i kow absolutely nothing about your game, style, and intentions....so please excuse the fact that yes i am throwing hand grenades at 20 paces... But figured it was obvious enough to suggest, seeing that your strongest ball on paper is the Nexxxus, yet is still weaker than your Maurader Madness according to the order in which u listed your arsenal.
If you think you might be interested in the Reax V2, pm me... As we just got an amazing deal through our distributor in which we can sell them NIB for as cheap as $130 shipped.
