Tone controls -- assuming you're ok with them, when would you try them?

The Loki is absolutely appropriate for a "high end" system...it's the cleanest and quietest EQ I've come across in decades of home audio and pro audio experience, and although I use it rarely, generally to spruce up older vinyl, it's an amazing thing. I "EQ" my system by sometimes adjusting my subs here and there and the Loki isn't in the system at all until needed simply to keep cable runs shorter (I put it between my preamp and amp...no loop available)...Don't fear the Loki...

The disadvantage of using the tape loop circuit (vs preamp/amp or source) is that there will be 2 extra sets of interconnects vs. one extra set. You may spend more on the ICs than the Loki, and have more cable degradation.

At what point do you go for tone controls? 

When you don't like what you are hearing.

As it has been said there are no laws that dictate how you have to listen to music. You are not going to be arrested, tortured, killed or thrown in jail  for using tone controls or room treatments or power conditioners or whatever. The only one you have to please is yourself and maybe your spouse or S.O. Anybody else's opinion not only doesn't matter it shouldn't matter. If using tone controls makes you happy use them, if not using tone controls makes you happy don't use them, but don't let anybody tell you one way is correct and the other way is wrong.

I asked a local dealer about the Loki; he has a couple dozen older equalizers for sale. He pointed at a shelf filled with them and wondered why anyone would need to buy a new, 4 dial equalizer, when they could easily get 5, 10, 30 band equalizers on the used market.

A quiet EQ with carefully selected parts is better than at least half of the old school EQ's. Especially the analog pro Behringers for instance.  

Eirk is correct about Behringer. They are to be avoided.

If you were interested in going the analogue 1/3 octave (30 band) e.q. route, you will want to look into Klark-Teknik. The DN360 has been the industry standard in professional music reproduction for decades and can be found used on ebay very economically. Other brands that could be considered alternatives would be BSS and XTA with an honorable mention going to Rane.

The thing about a 1/3 octave e.q. is that it takes a little practice to know which fader to adjust to make the change you want. A better way to look at a 1/3 octave e.q. would be to use it as electronic room treatment.  You would tune you system with the e.q. to your room where as with room treatment you are tuning the room to your system. Ideally if you are not opposed to tone control you would use both. Of course a tuned system nor a tuned room will completely fix those bad recordings so using the Schiit Loki at this point could be a very effective solution.

Preamp ----> tone control ----> amp ?

This is the best way to insert an external tone control. This is very easily done if you have separates.

And for an integrated, I'm not sure I understand.

In order to use external tone controls with an Integrated, the integrated would have to have either a preamp out and in connectors or a tape loop out and in connectors. This will effectively give you the connection as above. Preamp-Tone Control-Amp

Tone controls, room treatments, power conditioners, interconnects, etc. etc. etc. are just tools that are at your disposal to use in your quest to the holy grail of sound reproduction that you desire, if you want to. Nothing more, nothing less. I recommend using whatever makes you happy. 

I personally use tone controls to boost the bass at lower volumes and boost the treble a bit.

Reasons:

1) For the treble, because of our age, we lose hearing at higher frequencies.  Anyone who denies this must come from another planet.  So, it compensates for my loss of hearing at higher frequencies.

2) For the bass, the human ear does NOT have a flat response like the output from an amplifier.  Far from it.  At low volumes, bass is not as hearable as it would be at higher volumes.  It is just the way our physiology is.  In the 70s that is why the "loudness" option was on the devices.  I wish they would bring that button back.

So, my advice to the audiophiles who convince themselves adamantly that their hearing response is a perfect horizontal straight line, I suggest making an appointment with a hearing specialist to bring you down to the real world.

Thanks for the illumination, all!