The under-seat box belongs to (what is probably) the Matsu****a IFE.
The reason they can't be installed underfloor/overhead is, as I understand it, due to cooling requirements.
Agree wholeheartedly about the legroom issue, it really is a problem as these new systems are rolled out. The system allows for movies on demand and loads of other whizzy bits, but it appears to have been missed that pax would rather have legroom given the choice (or both, if the design of the hardware was properly thought through).