If they have speaker outputs, they are integrated amplifiers, which have power amplifier and preamp together on one chassis.
Preamps DO NOT have speaker outputs; only line-level outputs to go to the input of a power amplifier.

The "pre out" jacks of an integrated amplifier allow you to just use the preamp section alone with any other power amplifier; the "main in" allows you to use the power amp separately. For normal integrated operation the "pre out" is connected to the "main in" and they are used as a combined unit.

If you get an integrated amplifier that has pre out jacks, you can use the preamp section either with your current power amplifier, or the one in the integrated amplifier.