A rule of thumb: EQ's are best utilized in the "cut" position than the "add" position. Adding increases the drain on the power amp. If you boost a range by ten db, or twice the apparent loudness, you increase the power draw on your amp ten fold. That can quickly suck many amps dry.
A brief explanation of the difference between connecting an EQ in the tape monitor loop and the between the pre-amp and main amp stage.
First, all EQ's generate noise. Period. End of discusson.
The tape monitor is before the volume control. Since the volume control, by nature, is an attenuator, any noise generated by an EQ is attenuated before going through any amplifier stages. So, unless you run your pre-amp at full volume, going through a tape monitor loop minimizes any noise generated by your equalizer.
If you go between the pre-amp and main amp stages, any noise generated by the EQ is fed directly to the power amp at full strength and it's full impact can be heard on the final result.
By using the tape loop you bury the EQ's noise floor below or close to the noise floor of the entire system.. By going between the pre-amp and main amp you get all the noise generated by the EQ.
Given the option, I'd go via the tape loop method but sometimes you don't have a choice,