1. Regardless of being hardware or software, there are two classifications of EQ; multiband control and parametric. The former is restrictive compared to the latter. Both lower the overall output (maybe increases when subduing certain area?)
Yes, graphic and parametric.
Graphic can have anything from 3 bands to over 30 bands.
For tone control 3 to 5 bands is practical. For FR correction of a headphone it is not.
A 30 bands can very well be used for correcting headphones.
The biggest issue is WHERE does one base the correction curve on ? Differences between measurements of several folks can vary several up to many dB which will yield a different sound.
Parametric EQ usually only has just a few filters but they can be set to correct irregularities in headphones more accurately.
Here too the biggest issue is WHERE does one base the correction curve on ? Differences between measurements of several folks can vary several up to many dB which will yield a different sound.
In both cases, when fully digital the overall output is (or has to be) lowered in level when a boost in an area is needed.
When only attenuations are needed (unlikely) then an overall level drop of 1 to 2 dB may still be recommended.
Note that EQ
only can address FR related errors. Resonances, break-up, or deep nulls nor very high peaks can not be corrected.
You can't polish a turd.. You can't turn an HD201 in an HD800 and tuning a HD800 to the FR of an HD201 will still give 2 very different 'HD201's
2. There is no fundamental difference between hardware and software EQ, at least considering the ultimate output.
According to this information, it might suffice to just tinker with the software EQ.
There are fundamental and practical differences between software and hardware EQ.
Both have aspects that can be seen as positives and negatives.
Crappy digital EQ programs exist and so do crappy analog EQ's.
Remember... almost all studiorecordings out there have plenty of digital EQ already applied to it.
Personally I prefer it analog, but that's just me.
It does not require dedicated equipment, can use simple but good players or any analog source.
You don't need a PC, tablet, phone or expensive DAP that accepts plug-ins.
Of course there are also plenty of ADC -> digital processing -> DAC solutions around that don't cost much as an alternative.
My recommendation to you is... play around with multiband EQ and see if it get's you where you want it to be.
Or try some parametric EQ plugins.
There is nothing more educational (and frustratiting) than trying to EQ something by ear.