You nailed it it's big, it's ugly, and it's noisy.
You're going to have to remove all the moving parts especially the fans, put
it in a slimline That's capable of hiding inside some other piece of
furniture while still providing cable access for your display/TV and mouse,
There are several websites that address building silent PCs. You'll have to
look them over.
Being big is solvable provided you don't have too many add-on card's. You
need a motherboard, and a graphics processing unit. Other than that your
ethernet, Wi-Fi, sound should all be built-in on the motherboard.
Storage: get rid of your hard drives and switch to solid-state storage. Not
only is it quieter it's also cooler. Cooling is going to be a very major
The noisy this issue is mostly because of fans. Cooling a high-powered
system without fans is difficult. You stated you don't want to deal with
water cooling which would be one obvious way to go, and that probably leaves
out oil cooling as well. This leaves you with a combination of passive
cooling systems, very very very quiet fans, and a lot of soundproofing.
The quiet PC websites have products for all of these.
My solutions in the past have included placing the tower inside the bottom
of a TV platform, on top of rubberized mounts with lots of acoustic foam and
replacing all of the fans with models designed to be extra quiet.
The larger the piece of furniture you can place the tower inside of, the
more acoustic soundproofing you can place around. You still need to be
careful to designing your path because you will still need cooling.
Doing this well, in a way that still allows your unit to be adequately
cooled, and provides good cable access which is part of the performance no
lag issue is going to require some fun in improvisation.