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
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.
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.


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?
Just use a switch. You could also add a power conditioner with a separated 12v trigger. What about a wi-fi outlet?