So I was thinking of using a PC as my HTPC and using parametric EQ software (such as Equalizer APO) but I'm not sure if it can EQ all 5.1 channels independently and have global EQ when watching Bluray movies or Netflix ect.
Yep.
See the Equalizer APO documentation. Just have the global EQ first in your config file, then add "Channel: 4" to apply subwoofer-specific EQ. Or you can explicitly declare all channels, whichever you prefer. You can also do neat stuff like delays to time-align each channel to your listening position. If you want different EQ for BluRay than for Netflix, you can have multiple config files and use the
include directive within config.txt to choose which config you want active. Or if you want to get fancy, use
If / ElseIf / Else / EndIf to define your desired correction based on input channel count or sample rate, since your BluRay drive is probably multichannel, whereas Netflix through a browser is stereo. Buy yourself a calibrated mic and get to measuring.
The only benefit to a miniDSP would be if you use sources other than your PC, which is no small thing to consider. If your only source is now and will only ever be a PC, then Equalizer APO and a measurement mic ought to be all you need. If you do plan to use a console BluRay player, a Roku, and other dedicated sources while using your PC as an audio preprocessor, I'm afraid I don't have any experience with that.