If the receiver has preamp-amp jumpers you can connect a power up. The receiver amplifier would be bypassed. If you don't have preamp out on the receiver there is no easy way to use an external amplifier.
5 responses Add your response
Depending on your model, you can do "both." You can add an extermal power amp while still using the internal amp for a bi-amping configuration, assuming you have bi-wire loudspeakers.
This was a nice feature of the C series receivers and power amps. These receivers had a "matching" power amp so you could combine them and know that gain would be the same for both. The pre-outs of the receiver could feed the power amps.
In fact, I think these receivers even had an adjustable gain control so you could level match a different power amp (instead of using NAD's matched set).