I have done literally all that was asked of me(several times over), and for the love of god, I cannot get the sd2snes pro menu to work(2nd cart now). I have been through terrible hardships with this piece of shit, and there is a long backstory and screenshots and videos to go along with it all. Basically, at this point, I would appreciate it if someone would be able to hold my stupid hand and start from square one asking me pertinent questions that would aid in diagnosing why my SD2snes refuses to work. I won't list my exact setup, because I need a serious nerd to figure out why my setup isn't working with as little information as possible via the scientific method.
(Solved?) Had to literally get Akari_01 to (very kindly)make me a firmware that bypasses the sd2snes menu to run the burn in rom cart, which notified me that I have cpu failures: mpy 8x8 and div 16/8, both of which are not tested for in the diagnostic firmware. As it turns out most games don't use this function, and it's typically reserved for only some mode-7 functions, which is why most games work fine and the sd2snes does not. Hopefully, in the future the sd2snes diagnostic firmware will be able to test for these sorts of CPU errors so people don't have to get akari to write them firmware that bypasses the sd2snes menu just to get the thing that tells you what's fucked up with your shit.