#1 I'm not sure how to respond to this one.
First of all you usually "softmute" or "partialmute" in order to either issue a command, or to allow the TTS to be heard above the sound of other media. It is not really intended to be used to reduce the TTS volume. There is an action that can set the TTS volume though.
The partial mute setting in VC options means nothing unless you add an action to your command to perform a softmute. Also if you are playing video with digital passthrough audio this will have no effect anyway. There are several partial mute or softmute actions as well. One for MM, one for iTunes, one for XBMC and one for the system audio. Perhaps there are others I have forgotten, although the level that you set in VC options is just for the system volume muting. You'll need to explore a bit and then try to be more specific if you want help with this one.
#2 - You should be able to set your default TTS output device in windows settings, but you can also use the VC action: TTS.SetOutput
http://voxcommando.com/mediawiki/index.php?title=Actions#SetOutput