I was not enjoying the performance until I ......

You will have to adjust on each recording.

Who is this you?

Given most speaker cables “character” really is a matter of “tone control” as are most things we tweak in this game, a separate tone/eq is a worthwhile discussion. However, I also agree the first and foremost thing to do is get the overall symmetry of the system as dialed as possible. Then, if additional tone tweaking is what your ears want to hear, go for it. I’ve become a BIG fan of less is more in terms of overall equipment. Each cable introduced adds another potential for interference, noise, etc. more power cables increase the chance of ground loops. If these things get introduced, regardless of why, a tone control becomes pointless.

Again, I agree. Getting your system in balance is first and foremost.
It is the goal of every audiophile.
Sources should sound right the overwhelming majority of the time without equalization. It’s just the odd CD or stream that doesn’t make it that needs help.

I have not had any tone controls since the early 70s. I can't say I miss them but it's just a personal thing with me. If it works for you that's fine with me. 

System in sync? Nobodies system is in sync. Even under the best of circumstances there will be +- 5db variations in frequency response. Worse, the left and right speakers will not be exactly the same causing havoc with imaging. Impulse testing and digital frequency response control are the only way to deal with this. Once you know what perfectly flat sounds like you can make modifications to suit taste. You can see this application on my system page. I do not change response for various recordings. I prefer to listen to what the engineer intended. My system is so detailed I can almost always hear through to the instruments even listening to such stuff as Lois Armstrongs Hot Five and Hot Seven.