I guess you would have to open the receiver and have a seasoned electronics guy tap into the circuit board between the preamp and amp, disconnect the two and route the preamp's audio path to a set of RCA output terminals.
If your CD or DVD player has variable output level control, you can connect this directly to any power amplifer. THis is actually prefered by many purists if you only have one source to use, bypassing the electronics and switches in a preamp. But your source must have an output level control to serves as your volume control. CD players usually have 1v to 2v output good enough to drive the amp to full power. Many power amps have input sensitivities of 1.2 volts to reach full power.