The problem with SLI on laptops is having the room and a cooling system designed for the heat.... the support for this on the chassis, is generally only provided on the top two tier GPUs, sometimes lower ... right now that would be the 970M and 980M. For example.
Gt 840m could SLI with another Gt 840m but definitely not with cpu integrated gpu from another manufacturer. though AMDs apus can Xfire with a separate AMD gpu
Gt 840m could SLI with another Gt 840m but definitely not with cpu integrated gpu from another manufacturer. though AMDs apus can Xfire with a separate AMD gpu