Rather than saying that the 1400/2400 do not support 4-ohm speakers, I'd say that none of the folks around here know if they do. Yamaha claims they do and I think it's reasonable that they do. I've not heard of related 4-ohm problems given by the 1400/2400. I personally won't feel bad about hooking M80s up to my 1400 when I've the money to do so.

As far as other Yamaha receivers (HTR line, et cetera), YMMV.