These drivers seem to be unobtanium, but I got into posession of an Olivetti Envision P75 that has that chipset, and a working setup on the HDD so I took some effort to extract the driver from the system.

I included a text with some bits to put into CONFIG.SYS to get DOS stuff going. I edited the INF not to update the startup files, as otherwise it happens every boot.
I am not sure what will it take to get the voice sample not to play every startup, there should certainly be a way to stop doing that, at least in I saw in OTI601 driver install. Perhaps someone can chime in, I imagine 601 driver parameters are all same as 605.

I hope this will ease the pain of others who will have to deal with this chipset ~