Yes, removed the carbon fibre piece & cut the rubber out with a craft knife. Once I had that hole I did a keyhole surgery with the sabre saw. I cut up and around in U shape. I'll see if I can take a photo up in behind if you like.
Yes they are ballast switches, I have black rubber booties which go over them now so they look more factory.
That is the stock position for the speaker, I only have a grill there, the only speakers I have in the boat are subs (a 10" in the rear locker & 12" at the feet), everything else is on the tower. 2000W in total. I like it a lot.
I would advise against speakers in the walk through, my last boat had it and I wouldn't do that again.