Plex worked great for me in-network, but I had a hard time getting the remote streaming up and running, even after clearing the way with port forwarding and signing up with myPlex or whatever. I don't know why, but the emit app (lesser known, simpler version of what Plex does) worked nicely when remotely streaming through all firewalls so long as I set up port forwarding correctly. I don't know if emit works with .wtv files, I don't think it does.
Some other options:
If you have a rooted phone, you can install CIFS manager and play movie files on your Windows machine as if they are on your tablet, so long as your serving machine is on the same network or you're vpn'd. Anything that your tablet can open with any app is available as if it were right on your tablet. The advantage of this over something like SAMBA share support in es File Explorer is the compatibility is across the board...your tablet doesn't know the file isn't on its own internal drive.
Believe it or not, the newest version of Splashtop ("THD" or "HD", iirc) works great on tablets equipped with the hardware to run it. It's more a remote desktop app, but it scales and streams 1080i .wtv recordings no problem, on-network or remotely, so long as they are set up to autoplay in WMP as opposed to WMC (Splashtop has a problem with natively full-screen apps such as WMC).