Another Speccy game with digitized speech is Chase HQ:

https://youtu.be/yjrbcLm78I8?si=GMIqDdL31hq4ik72&t=87

Although tbf apparently that's done via the AY sound chip of the 128k, which is a lot easier than through the on/off beeper of the 48k since the AY can do digitized audio via CPU-driven volume modulation.