UV Mapping / Lightmap Problem

Hi Guys, This is my first post to the forum as I have hit a snag in my workflow that I cant figure out and was hoping one of you may have come across this issue.

This is my first project using unity and Ive been happily light mapping from 3ds max and Vray, importing these maps into unity using the UV channel 1 for textures and UV channel 2 for lightmaps. See WIP image below.

Now the client has asked for the ability to alter the stitching on the chairs in the scene. So we have set up multiple textures for each stitch so they can be mapped onto the seams.

So Ive gone about this like I have the rest of the scene but cant get the mapping of the seam and lightmap to work together. see attached.

All I have been doing is swapping the UVs on model import to get the lightmaps to work but I then lose the seam mapping.

I tried adjusting the channels multiple times, tried them attached as one object with the chair and separately, Ive tried removing the polygon Ids in 3ds max as well.

Any ideas? Thanks