After doing some other things I returned to my SA-8, and have some info I'd like to share. I draw a comnplete schematic of the circuit to get a better understanding which clearly showed some unused connections in the button matrix. Adding these buttons gives you 75! extra sounds (so all the sounds from the SA-1), 3 more demo's and a cowbell. There are still a couple of connections which don't seem to do anything.

To get all the SA-1 sounds do the following:
1) rename the original Tone buttons so the numbers correspond with the ones on the SA-1.
Tone1 -&gt; Tone0
Tone2 -&gt; Tone1
Tone3 -&gt; Tone2
Tone4 -&gt; Tone3
Tone5 -&gt; Tone6
2) add buttons between the following pins of the OKI chip:
26-15 -&gt; Tone4
25-11 -&gt; Tone5
25-13 -&gt; Tone7
25-14 -&gt; Tone8
25-15 -&gt; Tone9

For the 3 extra demo's add buttons between the following OKI chip pins: 24-15, 24-16, 24-17.

And if you need more cowbell add a button between pins 23-12 of the OKI chip.