There's a CLI that writes WAV files. Build it from the source with your own ROM:

make extract ROM=path/to/banjo.z64
make bkvsay

out/bkvsay hello.wav -p 0x0C "Hey Kazooie, look at all these notes!" -p 0x0D "Whatever, Banjo."
out/bkvsay --list                        # portrait ids
out/bkvsay -s 42 -r 44100 out.wav "..."  # fixed seed, 44.1 kHz
out/bkvsay --hold-a 1:3 fast.wav "..."   # hold A from 1 s to 3 s (also --hold-z, --hold-b)
out/bkvsay --no-ui quiet.wav "..."       # no box sounds