The voice is AT&T Natural Voice NeoSpeech Paul 16 at settings -3 & -3. The reader is not a human voice. I couldn't find any audios of these books so made my own using TextAloud. Not that great, many errors, could be better, but still better than any other audio of these books which I couldn't find. Many of the Kzin names are spelled out rather than spoken because the TTS program couldn't recognize them as speech. 
 
The numbers before each story indicate the chronological order (although the file did not load with the correct numerical sequence) and it's best to listen in that order. Appears to be about 200 hours total. I'll be finishing the Known Space Tales & short stories, not found in audio elsewhere, in the near future.