I'm using MFreeformEqualizer for system equalization on speakers and headphones.
It's a plugin, VST, VST3, AU and AAX, 32/64 bit, Win/Mac, made by Meldaproduction (currently half price, £21). My Audio hub is an ASIO DAW running on Windows.
It's a bit different to typical equalizers, in that it doesn't have "bands" - the equalization is continuous, and so you can simply draw the line of the curve you want and this is precisely represented in the output
You can also build the EQ profile using points and curves.
You can also import an EQ curve.. What I've been able to do in the image
above is, using a spreadsheet, take a text-exported measurement set (averaged and optionally smoothed) from REW (captured using UMIK-1), invert that response and translate it into the text format used for MFreeformEqualizer.
Once it's imported, I end up with an exact mirror image of the unequalized speaker response. Using plugin analysis tools I can see that the actual equalized output from the plugin matches the curve with extreme precision.
After some manual edits to the curve (e.g. chopping off boosts where room nulls are being chased too far, removing frequencies below the speakers' capability) I have got the best results for system EQ yet.
The plugin works in Minimal Phase (zero latency) or Linear Phase (~175ms latency). Oversampling can be set from 1x to 4x.
I'm due to do a recalibration soon, after moving some things in the room about, so I can do a more in-depth post on this process with screenshots etc if anyone's interested.