Thank you very much!
The truth is that, when I saw there was an answer I was a bit scared. It could have been a second attack by angry Apple fans mad at me for I still don't know what reason.
Thank you for your suggestions. I remain with the DAC0800 family but if I find it not working as expected I'll study again a quad-dac integration. I considered them but I didn't know how to solve conflicts in case more than one channel tried to write at the same time... But I'll consider them again after testing. I used a TDA2003 as amplifier. It should be enough for a 4 ohm speaker. And sure, I'll take a look at the PICSynth schematics. They look interesting.
My expectations on those first prototypes are not high. I expect to have to patch them in a way or in another in order to make them work (that's a Russian roulette) or to improve their performance.
Thank you again!
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Im happy to see that someone tries to make a PIT based basic sound card as well.
The DAC0800 is an old design and is not very easy to master.
The TLC7226 is cheap ($1 per chip) and can be directly accessed by a MCU since it has internal address decoders and latches. It is perfect for 5V peak analog output and only needs 12V and 5V to work reliable. I got a bit less than 4.9V peak (FF) from the analog output with 5V reference from a LM78L05 and it is very stable with little noise. The amplifier part of the MC16 is pretty generic and the TDA2003 is as good as any other AMP. If you use any analog reference voltages, try to get them from separate voltage regulators! don't forget chip decoupling since you will likely have no separate analog ground. You will get a lot of noise otherwise. Every digital chip should have a 10nf decoupling cap to reduce noise. You can create separate power zones by using multiple LM78L05 (a bit overkill 
).
You can try to build a prototype on a breadboard first (worked for me very well). You can use a Microchip or ATMEL MCU to test the function. Try to get the basics out of the way first. Auido-stuff can get complicated at times since leakage and different voltage levels can make things very difficult. Leave that for later until your digital system is working. Start simple and get more complex later on.
The PIT is very easy to program. Get that running first. then add the DAC and evolve the design step by step. You will only burn money if you directly start off with a complex design on a PCB prototype. If you have a working design for part of the features, make a PCB module with input and output leads for further prototyping.
The waveshaper part will be really 'ugly' as you want to change the parameters via software. Make modules with dedicated functions until you have a working prototype... If you have everything together, you can try to think everything down to a single PCB. That alone will be a tough challenge as digital and analog parts don't like each other very much
You will never get the correct 1782Khz quartz like the MC16 uses.
Just use 1Mhz or 2Mhz for the basic PIT clock or try to get a 3560Khz (or 3562.5KHz) quartz to get close to 2x the MC16 clock. Don't try to use resonators (they sound really bad).
These are just helpful meant comments. I don't know how much you have developed in the past and you might already have a good grasp on how to archive your goal.
Im very interested in your further work. Don't get angry or frustrated if you get bad comments or someone is making you angry. These are often only misunderstandings. Most people here likes a nice retro project like yours 
-Jonas
. I thought it could help but it was maybe a bad idea.
...schau, schau - Bilder sagen mehr
Und mit Dokumentation & Originaldisketten! 
