I've designed, built and operated a couple of recording studios -- and the principles for a good dedicated room for AV and for a studio control room are the same. Lots of info on the net and several good books on acoustic design that will give you ideas. MeToo has it right -- pretty cabinetry does not a good acoustic space make. Key is minimizing reflections (bouncing the sounds off hard surfaces so you get unwanted reverberations), so you want to create as big a "sweet spot" as possible that will concentrate quality sound (unreflected) with good visual site lines. Basements are often unhandy spaces because you don't really want a low ceiling -- that maximizes unwanted reflections. Go to the cinema and look at the rooms, even in the multiplex -- higher ceilings, slanted walls, wall treatments with soft absortion, some irregular shapes that act as diffusers, mixed harder and softer flooring and seating and an irregular ceiling, often with more accoustic treatment -- corners are filled in too, because they can catch and bounce around sounds, expecially long waves like bass. The lower the frequency, the longer the sound wave forms, so a small room volume will always suck for good bass response. Vibrations can also hamper a good listening room (your furnance in next room of the basement rumbles on, your refrigerator above kicks on and the main members of your house carry the vibration to your AV sanctum).
All that said, a lot of careful planning, working with basic dimensions of good acoustic principles, some insulation and acoustic treatments and you can do something. Count of spending several thousand dollars to get it right -- and that will be just in the room construction.
Finally -- don't believe the hype about cables -- many professional audio publications have debunked the cable myth. Don't use lamp cord -- but you don't have to buy high in cables either -- it is a waste of money. You can find some of the blind testing done by Mix magazine with the best recording engineers in the world listening to great equipment in carefully acoustically designed spaces -- with only cables changed -- net result -- they could hear no difference between cables costing thousands and those costing only dollars. It's the audio placebo effect (in case you can't tell this is one of my real pet peeves in the audio world). Frankly -- electrons don't care!
Good luck and have fun.