Other than an Atmos-capable pre/pro, I have all the necessaries to easily add 2 or 4 additional speakers to my main HT: speakers (RS Minimus 7s should do the trick) plus some extra NAD 2155 stereo amps kicking around. Thing is that the room is already full of "big" sound as it is (stretching literally from floor to ceiling), with great 7.1 localization, so I'm not (yet) convinced that I'm really missing out on anything. But if and when the Onkyo 886 ever gives up the ghost, whatever I replace it with will have all of whatever the current capabilities in a high-end pre/pro are, and at that time I'd throw up the extras, if the urge ever struck.
I can certainly imagine a noticeable difference in a bigger, and especially higher-ceilinged, room than my small main HT.
Jeff
ps. Are you two (Elf and C) running dual subs in a true .2 mode, and if so do you think it's sonically noticeable? I've got multiple subs in a complex bass-management arrangement but I still only have a single (.1) LFE channel.