Note that Audio Control DOES have a 2 channel unit as well if you only need two channels and will likely be much less.
The older PAC unit uses transformers and resistors to match the levels where as newer ones are all digital and optically isolated as I understand.
Not sure how to say this but the whine is caused because of the difference in ground potential between the amplifier and head unit.
One other potential issue...
In older trucks ('02 - '06) the BOSE system came in two flavors. Standard and Premium. I believe the Premium came in the EXT and the standard was all that came in the Avalanches. (I have not heard of any that did.)
The standard BOSE amplifier acts like an old power booster used to. It receives the amplified output from the head unit and amplifies it further. It uses a standard "turn on" wire. (Note when I ran this wire directly to my amps when my head unit was off I got a constant thump every 30 seconds when the key was on. Because of this I used the "smart" turnon that the PAC unit I have has.)
The premium amplifier took a constant line out audio from the head unit and is controlled through the datacom line to turn it on and to control the amplified level. Unless PAC (Or someone else) has an adapter to do this manually you likely won't ever get proper sound out of the system without using the premium amplifier. You can hook up the premium amplifier then use that to feed the correct audio to the Audio Control LC6i unit and then from THAT unit run your amplifiers.
Note that '08 trucks might be different. I do have documentation that covers GM vehicles up through 2009.
I have a 2009 Cadillac CTS that I am going through this with right now. Its standard 8 channel stereo is similar to the truck basic bose system, the 10 channel premium sound that the navigation system has uses a different amplifier that requires the databus connection and there is no adapter for it for my car so I have to use the premium amplifier. To power after market amplifiers I bought an LC8i which will combine the channels from the factory amplifier together and allow me to run a 2, 4, 6 or 8 channel system off it. Will accept I think up to 300 watt inputs and output low level audio that is compatible with standard amplifiers. They call it an OEM integration module i think on AC's site.
Anyhow if your only issue is the remote turn on then I just wasted a bunch of time typing but maybe it will help out someone else...