Years ago, I came across the term "corrective technologies". At the time, it was used in the context of home automation, but the presenter added that we apply "corrective technologies" to many things. Auto mechanics fix things that are poorly engineered, or just worn out. Doctors correct things in the body that are not working as they should. ER rooms fix things that can be the result of very poor judgement (possibly by others). Yes, there are hearing aids for hearing loss. And equalizers for frequency abnormalities.
To use medical terms, there are "acute" and "chronic" sonic issues with our systems. Acute issues are there temporarily. Chronic issues are 24/7, always present, reminding us that our system is not quite perfect -- yet. BOTH of these conditions can be helped with the right solution. But getting us to the finish line may require slightly different "corrective technologies."
Solutions can be multi-faceted in that a "one and done" may not get us all the way there There’s also the aspect of applying the right tool/technology to the problem. We don’t call the demolition crew to tear down a structure when an Kitchen cabinet upgrade is the desired outcome.
Many here have suggested working with the room, first. I think this is a valuable consideration. Maybe the FIRST consideration. IF the room is an issue, room correction will help tremendously with those "chronic" problems. But, also calm the effect of those "acute" issues (recordings?) thus minimizing their impact. Perhaps to the degree where you "take the exit" and you’ve reached an acceptable performance level. I’d also look at out sonic "warts" in the system such as the components themselves, cabling, power delivery, etc. I fully understand this could cause a case of "mission creep" where a perceived simple one component solution could grow expoentially. But, if you find the solution is in one of the above, then it is evidence that you found the right solution, as opposed to to putting a bandaide on a problem, thus masking inherent problems in the system/room.
So, if all the above points to the direction of an EQ, I would go with separate L/R controls as some have suggested here. Remotes controls are cool, and convenient and allow you to do instantaneous comparisons from the "money seat". (The seat where the person with the money sits.)
There was some mention of tone/level controls in vintage speakers. I am a proponent of conserving the looks and function of vintage gear. I also like to squeeze as much performance as I can out of these vintage pieces. Our practice is to bypass tone controls and replace them with high quality resistors, experimenting with values until we get a flat measured response (and, extended listening tests). These, invariably will provide less dynamic compression, improved detail and focus, and wider/deeper soundstage over the factory tone controls. It’s nice that the manufacturers of the day thought through the problem of their product being placed in a variety of environments and allowing some user correction (or, personal taste). Modern speakers have gotten away from this for a reason(s). We don’t see speaker fuses on receivers these days, either.
There are no right or wrong answers to the OPs question. Just a matter of the application of "corrective technologies" to provide the best sonic bang for the buck;.