I don't know what you mean with this. Strudel is AGPL, which is hardly "impossible to use on anything". The default sound banks are CC-by(-sa), CC0 and unspecified. The unspecified ones might indeed be a problem, but the other ones are fine.

As long as you allow anyone to get the source code of any derivative work you make of the Strudel code, and you take some measures to keep the distribution of the two works somewhat separate, you're should be good. And yes, there's a lot of FUD by the FSF, but your pet projects shouldn't be encumbered by such a narrow reading of 'derivative work'.

How exactly does the license matter if you just want to make music?

I think the underlying Supercollider sound engine uses the more restrictive GPL, though...