For some reason, bash on windows (at least the one that comes with git) executes some programas without attaching them to the tty. Now that I think of this, probably it just calls win32 with external executables.

output is not a tty

The solution is fairly easy, definitively you don't need to modify your code. What you need is to force bash execute them:

bash -c 'software parameters > "20160915 - output.txt"'

¡Note the nested quotes!