Your room is definitely the weakest link. Or rather your belief there's little you can do. Acoustical treatment on the ceiling, is as important as the walls in controlling both early reflections and overall reverb and slap echo. and using panels covered in cloth to match the ceiling, they are virtually invisible. Wall panels can also be covered with artwork, and even your own photos.
Corner bookcases offer a tremendous opportunity to integrate absorption, diffraction and bass traps into their design. Think an 'L' shaped piece divided into cubbies, some filled with books, others panels either facing straight on or slabs on edge - mixing it up.allows a lot of tuning options. Using two intersecting flat cases would leave a 12X12 rectangular space (assuming a 12" deep bookcase) that could house invisible bass traps - passive or active. Even doing some of this will yield far greater and immediately audible improvements for a fraction of cost of any electronics changes or re-cabling.