As above, the USB socket is only for power.
I have a Microserver (N40L), with Serviio installed, along with BubbleUPNP server.
I am using BubbleUPNP (paid for version) on my Nexus 5, Nexus 7 and my old Andypad.
The settings I use in the BubbleUPNP app (under ChromeCast) are:
Video Encoding Speed - Ultra Fast
Max Video Bitrate - 4000
Enforce Max Video Bitrate - Checked
Preserve Multichannel Audio - Unchecked (The TV I have my chromecast in doesn't have surround, so a waste of bandwidth for me)
This produces streaming DVD ripped MKVs without any loss of perceivable quality as far as I'm concerned. I've yet to try BluRay rips, but I only bothered ripping a few, and those stuttered over the wired LAN, so guessing Wireless won't be anywhere near as good as that!