Connecting avr preout to amp using Y cable

Have a 5.1 system but a 4 channel amp. Three channels taken up by 2 fronts and the center; want to use the 4th channel for rear speakers. My avr preout for rear has positive and negative rca terminals. Can I use a Y cable to connect the rear preouts to the 4th channel?? ie the 2 ends connect to preouts and the opposite single end connects to the 4th channel. Any suggestion is appreciated, Thanks
DD5.1 requires 5 discrete channels, plus LFE output for a sub. If you have a 4 channel power amp, I would suggest you use three of those channels for your front L&R speakers and center channel. Use the receiver's L&R rear outputs direct to the L&R rear speakers. Most of the sound, and power consumption, are for/from the center channel and front L&R speakers. Powering the 2 discrete rear channels directly off of the receiver should be fine.

Don't forget to re-run the setup program after you insert the 4-channel amplifier into the mix. The setup program should compensate for the added power being used for the front and center speakers.