Surface pro 3 ...arfr

The best option for this hardware is an ETCnomad dongle, and install the full Eos Nomad.

This way you can have full control of your Eos (or Cobalt) system as a Client to it, as if you were sat in front of the console. It can also act as a full standalone 256-output Eos/Cobalt console if needed.
Your local ETC dealer can give you a price for this.

The next best is an OSC control application, however I don't know which OSC apps are good for Windows 8/10.

The best option for this hardware is an ETCnomad dongle, and install the full Eos Nomad.

This way you can have full control of your Eos (or Cobalt) system as a Client to it, as if you were sat in front of the console. It can also act as a full standalone 256-output Eos/Cobalt console if needed.
Your local ETC dealer can give you a price for this.

The next best is an OSC control application, however I don't know which OSC apps are good for Windows 8/10.

the two i know of are OSControl and MetroOSC, the latter can be found in the Microsoft Store for free.
Disclaimer: i have worked with neither and can't recommend (or warn of) them