Elements are logically separated into objects - only one multi-sub object material - attaching to one piece causes no problems.
The parts that need mesh/turbo smoothing are named 'Sub1' and 'Sub1-SG' if the smoothing groups check box is intended to be checked in the smoothing modifier.
Seat will render without any subdividing for medium backgrounds and further.
Topology is very clean so tweaking for custom needs should be easy.
main surfaces are unwrapped so creating custom textures is easy. If you want to create mismatched materials for cushions - different areas are easy to select by smoothing groups.
.3DS file included and a scanline version of the materials - obviously the shaders are not on the same level with the mental ray versions. .3DS version should be considered as raw geometry.