If you are drawn to the 805's, I would get them. Very little risk on your part at that price.
I like the Decco and have heard it power some nice Vienna Acoustics floor standers to moderate volumes without losing control. But I have heard similar amps under-drive the 805S and it was not very engaging, whereas an 80 wpc tube amp was heaven with the same speakers.
I like your idea of combining the Decco with the Emotiva amp to drive the 805's. I assume you have the Decco because you need the DAC? If not, I might suggest selling the Decco, passing on the Emotiva and getting the Cambridge 840A that is currently on sale on Audio Asylum to drive the 805's - a good value. Just a thought.