I'm having GTRetro87 recap and replace the chips on my X-Men board. He comes highly recommended at KLOV and his prices are excellent. While I could recap it myself, it's much lower of a risk to let someone with experience do it (in case problems arise), and getting the op-amp and DAC swapped at the same time for a little extra is perfect.
Definitely look him up if you need Konami sound work done.
As far as capacitors, I used to believe that voltage rating has nothing to deal with how the capacitor works except for how much it can handle -- but after reading more into it, it's been explained that the farad and voltage rating both work with eachother - the capacitor builds up, say 4.7uf at 16v or 3.525v at 12v (since 12v is what most PCB's use for sound).. now if there's a cap that's rated 4.7uf at 25v -- then at 12v it should be 2.256uf. See what I mean.. makes you think.
But hey, I'm not sure what the amp circuit needs but as long as it works and doesn't get hot -- awesome
As far as stereo - how do you have your supergun setup to speakers? directly connected? One thing you can do is build an attenuation circuit on either a SPDT switch OR on a breadboard to bring down the sound to a line level - check out Xian Xi's tutorials on Audio Attenuation when building superguns.
I will also take a pic as soon as I can and explain how I did my setup for my supergun, although it truly is superfluous and could have been done MUCH more simple.
Thank you SmokeMonster for the +1 . I've been through A LOT in 12 months over these Konami Hybrid Sound Modules, so I'm pretty avid now when handling these lol.