Unless your receiver is having trouble adequately driving your speakers, replacing it with something else will be trivial as far as sound quality goes. I used to run a receiver that retails for about $600 with speakers retailing for over $6000. I replaced the receiver with one that retails for about $1700 because I wanted more (and newer) features. Unless I engage a feature that affects the sound, it sounds the same as before. Now, the newer receiver can put out about twice as much power as the old one, but since my speakers are an easy impedance and normal efficiency, I could play my system loud enough to be painful with crystal clarity with the old receiver, so the newer one's extra power is useless for me. But, if my speakers were more difficult to drive than they are, it could have mattered, but in that case, getting a separate power amplifier to drive them would likely have been far better.
From your description, it sounds like you need sound absorbing materials in your room. You know how when you go into an empty house, there is an echo? That is very bad for playing music, so it is a good thing to have paintings, tapestries, curtains, etc., on the walls to help prevent the echo. Bookshelves filled with books and other things also help. Even hard things in the room break up the sound from simply bouncing back and forth between the opposing walls and the floor and ceiling, so being sound absorbent is not essential for everything in the room.
