HTB preamp and AVR turning on the same amp.


Hello, I just added an Anthem str preamp to my AVR Anthem mrx720 5.1 system. I've had a 12 volt trigger turning on my 5 + 2 channel amps when turning on the avr. Everything worked great. Now I need to turn on the 2 channel amp when I turn on the preamp only. I don't need to turn on the avr when using the preamp.
Can I use a y-splitter to connect both 12 volt out triggers from the avr and from the preamp into the 2 channel amp? The searching I've done mentioned having to customize the cables if done like this.
If I can't do this, I can always just have the preamp turn on every time the avr is on, but I would rather avoid that. Any simple ideas?
cissado
Thanks Fiesta. I do have a power conditioner that I don't want to replace to keep it 'audiophile friendly'. All the components seem to have 12 voltage triggers in and our. I'm sure others do this, I just haven't come across it yet. I did email Anthem,  so we'll see what they say.
Does anyone know about the y-splitter cable?
A y-splitter cable will work. But it is better to install a diode (1N4001 or equivalent) in series on each connector to prevent possibility of damages if AVR and stereo preamp both turned on at the same time accidentally.


Thank you imhififan.
You've confirmed my fear that the cable has to be modified. I guess I can do it, but I'm still amazed how there's no plug and play solution for this. 
I may just opt for both AVR and pre to turn on together instead of customizing the cable. Still deciding, but thanks again for all the help.