Love your progress on whack a mole.
Just curious are you planning on reusing the original MPu and boards from machine or are you going proc and mpf route.
Secondly I notice you added the chimes into the machine. This may distract from your point sounds and mp3/wav sounds.

My assumptions with the retheme is you will want the proc and mpf solution.
This will completely take care of your sound effect direction.

If that is not the case I can make a few suggestions. In my case I did the Arduino mega and the raspberry pi route.
For me the Arduino was the brains and trigger sensing events. It transferred all game event triggers to pi and it played them back. The pi was also the back glass driver but everything was messaged to it real time by Arduino.

Let me know what your thoughts are. You can check out my Arduino conversion of Close Encounters thread to see what I did.

What are you going to use for the brain for your machine?
Double wiring switches is a lot of extra plumbing.

Robert,

If your not afraid of coding and hacking then the Arduino Mega and Raspberrry pi or mini windows pc.

If you want a slick mature home brew pinball solution ...
Use the Mission Pinball framework with one of the compatable hardware solutions
(proc, OPP, FAST, etc)

In my humble opinion, the MPF with PROC has a maturity level and online support plus forum support available.
The good news is the MPF frame work code will work with all of them.

The home brew section has a few threads on builders who documented their journey using MPF and Proc.
I am not biased to any of the hardware solutions so I’m sure you would do fine with any of the MPF supported platforms.

Cheddar,

One cool switch matrix I saw was to use the Spikenzie B64 solution. The was used by another fellow who did the Arduino conversion for black hole. The switch matrix was 8 x 8 that handled the debounce via hardware. He has a YouTube video of it.
Google spikenzielab B64 to see more details.
It’s the cats meow for using less pins on your Arduino and simplify coding for switch matrix.
It could also be your lamp driver matrix.

Check it out.

Robert,

If you want to build a component system using arduino’s you Could have an arduino that is for lack of a better word your sound board.
This uno would have your wave trigger shield attached to it. It could use serial communications to issue trigger commands like play wave file1 - wave file99. This would remove the need for extra wiring from your play field. You could easily component test it and later drive it using 2 or 4 pins on the board.
I used the same technique on my machine.
Imagine this... one uno may be used to drive your led score, credits, ball display, the second for your sound board, the third your master or brain.
For me I skipped this and went direct to using the mega rather then multiple uno’s cuz it has more usable gpio’s.
Any way that’s food for though. Using many uno’s allow you to learn the coding side and simplify the design into smaller bite size peices.