The problem you are going to have using the global inputs is that each channel has a switch that you select between line-in, global A and global B.

So if you're planning on putting Ipod on A and Pandora on B, be prepared to tell the client that they will have to move the little switch in back to change sources to each zone.

Why not just stick to the original plan but get 2 of the 240 watt, 70V amps. Put 8 speakers tapped at 15 watts on each amp to maintain a 50% power budget on each and use the loop out from one amp to the other.

This will provide all gain/volume control and source selection to the front of the equipment, which will be a lot easier to control for the client.