To my knowledge you can't set Nap 100 into mono mode
Perhaps its possible to use two of these by using one channel of each, others left unused, this should leave full psu to the single channel as someone once did using two Nap 250 into "Nap 125" mode, this will require a special cable though, Nap 100 has RCA so an easier task I'd imagine
Naim should however offer a full mono version of the Nap 100 along with a half width matching pure analog preamp, this would be cool but it will most likely never happen.
I use my Qute into preamp figuration albeit with a Nap 150X, more powerfull than Nap 100 but honestly I slightly prefer the voicing of the 100.
As for the Iota's the original bookshelfs are great speakers, never heard the Alpha, I hope they perform near backwall without boom, they are ported unfortunately, but so are latest Rega RX floorstanders and they have aparently solved this issue, indeed the previous RS5 boomed way too much in my room
When I had Motive 2 they did not accept placement close to any boundaries even they were ported downfiring