I build a
HTPC (Home Theater PC) using one of my old P55M-UD2 systems, and it's still running. A case like the
Silverstone GD06B, which looks like a faceless audio receiver, will fit nicely into your audio center. You can find newer cases (and, maybe, for less cost) that will take your components, but you'll have to have a small graphics card (like the ITX case type graphics cards) as this case won't take a large graphics card, IIRC.
If you decide you want to upgrade your components, I recommend a mATX motherboard with compatible memory and PSU, not to mention a graphics card that supports 4K HDTV. You will not be able to recycle your memory nor PSU. All the processors since Haswell require memory that's on the motherboard's Memory Support List and a PSU that is Haswell "ready" or "certified" or compatible with 4th/5th/6th generation processors. The reason is Haswell and newer processors have an idle voltage state that is lower than it's predecessors, causing older PSUs (like your Ivy Bridge PSU) to think the system is shutting down. Consequently, the PSU will move into it's shutdown mode.
Memory specifications require Haswell+ specifications, too. Thus, my recommendation to use memory on your new motherboard's Memory Support List (or QVL).
So, your choices are to a) use your Z77 system components with a HTPC like case and, maybe, a newer, smaller graphics card to support 4K screen resolution (HDMI 2.0 or DP1.4), or b) new system components with a graphics card that fits the case and has 4K display capability. I'd try your old components, first, as you know they work - you'll just need a new graphics card.
Good luck!