As B21 says, mmi behind the air-con and a small amp on top of the glovebox. I used to have, for a short time, a MULF on top of the glovebox, so there is room.
Your problem is going to be getting two y loom quadlocks behind the headunit. There is little room to start with, and it's a bit of a struggle to get one in there, let alone another one.
You may have to remove some more panels to see if you can re-route the original quadlock and put it in a better place, really not sure this is possible though.