"Can I mix microphone and other sounds before sending to netstream?"
try to use advanced sound card or driver, it's not an AS deal, it's just your system options
"Can I record audio from netstream without fms?"
you mean to record on the end computer? or what?
I don't know about the first one, but i would imagine for the second you can access the soundtransform on the netstream, and using a method similar to the new microphone raw access you could build up a byte array of the incoming audio, thus creating a wav of the incomming audio. You will probably need to enable the .audioSampleAccess on the publishing netstream.