If the factory system has an "aux in", you just plug the player straight in.

If the factory system has a CD changer input, you might be able to find an aftermarket adapter that will let you plug a line-level device in (although this is iffy).

At worst, you can use an FM modulator and use the factory's radio receiver to receive the empeg as if it were a radio station.

All of the above assumes you have enough room in the dash for the empeg along with your factory system. If you don't have room to mount both units, then you need to get rid of the factory system or find another alternative.

More details here.