I have a lovely big space behind the TV, a recess the other side of the chimney breast, so have plenty of room to hide stuff behind there. I have cables hanging down from the ceiling (ethernet and speaker) that aren't even clipped to the wall that don't get noticed. That big case that would look stupid anywhere else almost disappears behind there and is a convenient space to rest the router and door bell.

A re-purposed DVD player would be nice. Especially if you could fit some sort of LCD display.

The ebay seller I got the HP system off sent me the wrong one (8200 (Core i5 2400) rather than 8000 (Core 2 Duo)) so it's a much better spec than what I was planning on. But the size is ideal. Popped a cheap nvidia graphics card in there and my satellite tuner and it was good to go.

pretty sure it is, yes - I think it's great :D

It looks like something Captain Nemo would have had on the Nautilus! :)

What about actually building an enclosure/channel tunnel around the hot bits so the air moves through it but the sound is then broken up?

Imagine the red lines below as MDF/Chipboard for instance. These would be the same depth as the overall enclosure and you could but egg box in the rest to help deaden the sound.

That sounds like a good idea actually. It'll help with cooling too. I can also make the bits that cover the motherboard shallower and maybe put insulating stuff over the rest. Hmm, a plan for next year sometime. Thanks for that idea.

that is pretty much why I like it :)

That's proper steam punk!