If you MUST have layers in it, and it WILL open a tiff, then save the psd file as a layered Tiff. Try opening that.
Why do you need such a big bitmap pic in a vector program?
Try lowering the resolution or reducing the number of layers.
What's the finished size of the Illy file?
I've had 60 meg jpg files print out perfectly well at 8 x 10 ft size.
Alternately, do the opposite- keep your psd files in P'shop, and place the vectors into new layers in the psd file, then flatten whne you gat a chance, or save as a jpg.