i've been doing some research on the all in one idea and your needs seem to follow what I was thinking. The Anthem integrated seems like a winner from many standpoints. enough power, digital ins as well as analogue and then there is the room correction system built in, this is the main reason you would buy this amp and from all the research i've done that's what makes it so good other wise its just an average hi end integrated that you will either love the sound or not just like any other product out there. I think the anthem room correction is on par with the other well done room correction systems out there thinking lyngdorf .
Speaking of Lyngdorf have you looked at their integrated getting fabulous reviews and do all if not more then the anthem.
I personally was looking at the anthem pre amp with the room correction and the lyngdorf integrated amps. The anthem preamp may fit your bill for upgradability but you will need a 2 channel amp.
I'm not a Naim fan, I have owned an all Naim system but was never engaged in the music so dumped it all and returned to tubes. I just don't get the Naim sound I suppose I always found it boring and could never get past one side of a record before I went off to do something else. That's me though so everyone has a different story.