As said that wouldn’t make sense. The stereo stream is beeing compressed on the Performer end and sent to studio (and vice versa). So no, you don’t hear the uncompressed signal because if it could be transmitted uncompressed, it wouldn’t have to be compressed in the first place 
The reason why you doubt that is because for instance a vocal performance at 320 kBit can hardly be distinguished from the uncompressed version.
The audio stream from Performer to Studio is always stereo. For that stereo stream, signals are mixed within the recording section above the Performer monitor faders.
After recording you apply the “Get HD files” function which will transfer all recorded takes and create separate tracks (in your case, six) in Cubase where those takes are put. Thus, the max upstream rate for audio would be losslessly encoded stereo, see other mail.
Correct. stream from Studio to Performer is also always stereo, essentially the Cubase Control Room cue mix which also includes TB.
Usually the connection is peer-to-peer. When you connect, a connection server is involved but after connection, that isn’t active anymore except for disconnect. Thus, the “URL” is usually the IP address of your partner. In some cases relay servers are involved when router and firewall problems prevent a direct connection, but those practically never fail to receive and send packets.
With the new version comes a diagnose view which shows packet losses and audio glitches. Meanwhile connection quality has improved significantly, most of the times there are no losses except when using shaky wireless (WiFi, LTE etc) connections.
Hope that helps.