Texturing, nodes and UVs (multiple questions)

Hey guys. I’ve got the following render. Please excuse the unfinished macbook and the hover-keyboard!

Question 1)
I want to texture the speaker cover. It looks something like this:

They have a very thin semi-transparent fabric cover. So far i have a set-up like this:

The above set-up doesn’t yield good results. I was wandering what method i should use to create a semi-transparent fabric material. Any thoughts?

Question 2)
I have a picture with a frame (all one object) on the top left corner of the image.
I wanted to give the frame a teal diffuse / glossy mix shader and assign the picture to the centre face while unwrapping. I basically want to find a good way of assigning decals to meshes. I have followed a few tutorials with Attribute nodes while unwrapping but no success there.

What is do is this:

I create the above picture in gimp and give it a teal padding. I then unwrap the object in blender into the teal area and scale it down so it fits in there, and then i unwrap the centre face to fit the image without the padded teal area. Once again the result is not that good.

How can i have a mesh with a diffuse/glossy mix shader and only apply a decal on certain faces?

I know that i can just separate my mesh and apply different materials to it but i really want to learn to do it this way.

The picture was rendered in cycles. 4600 samples in an impressive 16hrs. (impressively slow that is)