Actually, I wanted to implement is, for each instrument, “lock to a note: C#5” for example, which I think would be versatile. However, one problem with that is the overhead for limited hardware such as Amstrad CPC.
There is a solution for you, though: instead of using “notes” for your drum/snare parts, simply force the software periods in the instrument, and don’t use Arpeggios or pitch within the instrument. The forced periods never changes, even with pitch effects from the tracks.
For example:
software period, noise
0 400, 15
1 420, 12
2 440, 10
3 460, 4
4 500, 1
5 auto, 0 –> Loop here
Here, you have a (crappy) kick drum and your bass note at the end. It is not very user-friendly, but you can find create a real instrument, find the periods that you like, and then create a less-friendly instrument like the one above, from it.