They really don't integrate too well with modern receivers.
These require a path out of the signal and a path back into the signal chain. In the good ole days of stereom they had what;s called a "tape loop". What this is is paif of outputs out to a, external device (tape recorder, equalizer, whatever) and a pair of inputs back into the signal path. When the "tape monitor" switch was out, the signal remained in the signal path within the unit. When it was pushed, the internal pats was broken, the signal was sent out to the device and then back into the path, after passing through the external device. So, what was sent out comes right back after passing through the device.
Modern receiver s generally lack this. The only way to insert an eq into modern receivers is between the pramp and the power amp, and not all receivers offer these. Quite a few offer pre-outs to exrternal amps and this would work, but fewer offer power amp inputs.
Many receivers do offer a "tape out" but these are not the same as a tape monitor. These offer a one way trips to a recorder with no direct return path. You must use the selector on your unit to select the external device's output just as you would select any other input. There is no loop.