hmm my thinking on this is that #1 would be ok if you could live with having to Power Off the empeg every time you leave your car.. this could get old fast.
#2 and #3 are really the same wire since the power control wire on your amp comes from the power ant output on the empeg.. this is probably a no-no since you don't know if the cd player you have draws a lot of power from the accessory line. I guess most CD players draw their main power from the battery but who knows you could have one that doesn't and drawing too much power from that power ant wire will probably do bad things to your empeg. What you really need for this is a relay.. a 12V relay that the empeg would turn on and off with it's power ant output. When it's on it would output the 12V battery wire to both your other head unit's accessory pin and your amp's power control. Of course the easiest and safest option is to buy a decent portable radio and hook it up to your AUX input on the empeg....