Calling sapiscr.exe doesn't invoke the "Speech properties" dialog. The complete command line to do that looks like this:
(This information was gleaned by using Sysinternal's "Process Explorer" and dragging the "Find Window symbol" on the "Speech Properties" dialog which was opened from the Settings dialog.)
"C:\Windows\system32\rundll32.exe" C:\Windows\system32\shell32.dll,Control_RunDLL "C:\Windows\System32\Speech\SpeechUX\sapi.cpl",Text to Speech
This works if windows folder is C:\Windows and sapi.cpl is located under C:\Windows\system32\Speech\SpeechUX.
Figure out what ProcessStartInfo parameters you'll need to set and
feel free to come back for more if it doesn't work out. You need to give us detailed information of exactly where you are experiencing difficulties.
Best Regards,
Manfred