The shelf equipment you suggested is available, luckily
In fact, at this point, I think maybe the best option is to motorize such a shelf and automate it based on the receiver state: the cubby opens up and the speaker moves out when the receiver is turned on, and goes back into the closet automatically when the receiver turns off. That would satisfy all the requirements - design, acoustics, and kitchen safety (assuming nobody's using the kitchen when the speakers are in use

).
Since the speakers are on spikes, there's no worry about the shelf resonating with them?