You can see my system below. Question is what thing(s) do I buy for Christmas? My thoughts are (in approx low to high expense):
1. Oppo 103D
2. Sonos Rack
3. Emotiva XPA5 or 7
4. Second SVS SB 13 Ultra
5. Vizio 70" M class
6. Projector/Screen probably Epson 5030 UBE and fixed screen (not high end)
7. Upgrade fronts to RBH 8300R
I'm renting a house, so future flexibility is important. The thing that bugs me the most right now is the 55" screen. I don't want to buy something that I'll want to replace in 2-4 years. Don't mind it too much if I could repurpose in second living area or master bedroom. Right now I'm 60% tv, 30% movies, and 10% music.
To me, your question hinges on
what is the proper size TV/screen for your room?
If it is 70", get the 70. If it is 80-90" wait a year (prices dropped quite a bit this year, but at 70" you are still in the $$bleeding edge of technology). If it is 120", get a projector (but I don't know lord helmet about projectors, so take that with a grain of salt).
We can't really gauge the comparative worth of the Sonus rack.
The Denon 4520 has a strong amp section, so I might suggest getting a two channel amp for the mains and letting the Denon handle surrounds and center. A pair of XPA-100's would get you more power for your mains than the XPA-5 for less.
Unless you are noticing issues with your current sound to indicate you need more power, I believe the second sub is most likely to make a readily audible improvement.
So my answer is
1) TV/projector as appropriate to get your final size, if it makes sense to wait (because the price of a 70" is liable to go down $500 or more in the next year - I would not buy it as a stop gap measure), get a
2) Subwoofer