Question 2: As you can see from the third product picture (view of the back), this unit is not equipped with a LAN connection.
Question 1: This unit has enough power reserves to cope with a wide variety of speakers. I use the more expensive predecessor model (MARANTZ Melody Media M-CR611) with Bowers & Wilkins floorstanding speakers, and the amplifier power is the same with the M-CR412. At most, the question is whether the KEF and Marantz character positively support each other's acoustics. Let's say a receiver is warm in sound, plays treble clearly but still pleasantly, is strong in midrange reproduction, bass sounds a bit soft, lackadaisical. But because of the high musical quality, staging, stage, etc., you still want it. Then it makes sense to find a pair of speakers that can reproduce the strengths, but compensate - at least partially - for the weaknesses. Of course, other factors play a role, but what I want to say is this: even if the Marantz can easily handle the KEF's in terms of amplifier power, the sound result is not necessarily as convincing as test reports can suggest. However, since these are compact speakers that tend to be rather slim on bass anyway, I don't really see any problems with this combination. On the contrary: the two brands seem to harmonise so well that there was already an official set with Marantz receiver and KEF speakers (LS 50) for the predecessor model.