FWIW, and equalizer is IMHO best used when it reduces the frequency output such as you seem to need, not to increase the signal strength as seen by your amp.
Consumer equalizers usually have 10 frequency centers spaced over the frequency range and each of the 10 divisions cover one octave (but it does not offer control of the width of the frequence it affects which, depending on the slope of the center's fall off, will overlap with the adjacent frequency control. This produces a rather broad dip (or increase) in the frequency response. I suspect that it would not be suitable for solving your issues.
For example, consider that you have a ringing in your hearing around 5K hz. A 10 octave equalizer would have centers an octave apart at 3200hz, 6400hz, and 12800hz. In order to reduce the FR at 5K hz you would also be depressing the FR at 3200 Hz and 12800 hz and your sound would take on a dullness to which you might object. It is possible that a 1/3d octave equalizer might be more helpful, as well as more expensive, for the obvious reason, but more complex is not necessarily better, because you may have more options but you still have less control over the width of a specific frequency.
I'm assuming you have problems which have a much narrower (than an octave) FR issue and that is where the parametric equalizer comes in. While one may have only 3 frequency center controls it has the capability of narrowing the width of the frequency response and minimizing the effect of a reduction at that frequency to the response of the frequencies surrounding it. Except for the effect on that frequency the presence of the equalizer sound not be heard. These are the most expensive equalizers.
Re equalizer insertion putting it between your amp and preamp should not be a problem unless you use it to increase signal strength substantially. Not your problem I think. Using a digital equalizer seems to be a good alternative to an analogue one but I have no experience using one. Its is something to consider.
Hope that helps a bit.
Consumer equalizers usually have 10 frequency centers spaced over the frequency range and each of the 10 divisions cover one octave (but it does not offer control of the width of the frequence it affects which, depending on the slope of the center's fall off, will overlap with the adjacent frequency control. This produces a rather broad dip (or increase) in the frequency response. I suspect that it would not be suitable for solving your issues.
For example, consider that you have a ringing in your hearing around 5K hz. A 10 octave equalizer would have centers an octave apart at 3200hz, 6400hz, and 12800hz. In order to reduce the FR at 5K hz you would also be depressing the FR at 3200 Hz and 12800 hz and your sound would take on a dullness to which you might object. It is possible that a 1/3d octave equalizer might be more helpful, as well as more expensive, for the obvious reason, but more complex is not necessarily better, because you may have more options but you still have less control over the width of a specific frequency.
I'm assuming you have problems which have a much narrower (than an octave) FR issue and that is where the parametric equalizer comes in. While one may have only 3 frequency center controls it has the capability of narrowing the width of the frequency response and minimizing the effect of a reduction at that frequency to the response of the frequencies surrounding it. Except for the effect on that frequency the presence of the equalizer sound not be heard. These are the most expensive equalizers.
Re equalizer insertion putting it between your amp and preamp should not be a problem unless you use it to increase signal strength substantially. Not your problem I think. Using a digital equalizer seems to be a good alternative to an analogue one but I have no experience using one. Its is something to consider.
Hope that helps a bit.