Yes, most accessories and upgrades that fit the other QB78 models will also fit the QB78S. For example, the XP Tune Kit, Oversize Bolt Handle etc.
The main difference I've seen so far is that the QB78S uses a different stock attachment system to the wood-stocked models. The QB78S has a third stock screw that secures the frowned and tightens into a new, different barrel band. If I can actually get Photobucket to work (don't ask!), I have some photographs taken to post on this Forum illustrating the difference.
Hope that helps.
Archer Airguns Inc.