I have my lovely light MB210 and after advice here I have ordered the 210MBE extension this morning
I will obviously need a Speakon cable to connect them, but unfortunately I have zero experience of these.
From googling I see that there are 2 pole and 4 pole versions of these and for most uses the 4 pole seems to be recommended but I can't find anywhere that tells me whether a 4 pole will work with this set up or whether I should get a basic 2 pole.
(I understand that there will be no advantage in this situation of a 4 pole but it may give me more flexibility if I change my rig later)