how to trigger my sub amp when main powers up.

Csm, if they were passive then the AVR would power them and he wouldnt need to power them.
I still am confused about a powered sub , right? That doesnt wake up when it recieves a signal.

From his description, I don't believe the subs are powered. He states that he is using a HK3490 to power the subs in his main speakers. The HK3490 is a 2 channel receiver. It sounds as if he is trying to biamp his mains using both the AVR and the amp section of a different receiver (the 3490). It also seems he wants both receivers to power up with the push of one button. It would be helpful if he would clear this point up and give some more detail about his set up.

Csmgolf is correct. I am bi-amping my nht 2.5i's which are very power hungry. I have a carver tfm15 which seems to sound exactly the same in place of the 3490. I may just use it instead. I'm hoping to find a good 5 ch amp one day to take care of the front 3 speakers. there seems to be no 12v trigger on the 3600 and i prefer to plug directly into the wall. thanks for all the replies.

If your gonna use the TFM15 you can just leave it on 24/7. It stays cool and wont use any real power when idol, I have had a TFM35 on for long periods with no issues.