For $3-4K as a budget, I would also consider revamping the speakers as well. Your ceiling is only 6.5' and you have tower speakers. I believe you'd have much better results sonically with a 3 piece subwoofer/satellite system (i.e. a really nice pr of monitor speakers coupled with a powered subwoofer).
Previously I also had my system in my basement with a low ceiling and it always sounded best with smaller bookshelf speakers that were low to the ground as opposed to floor standing speakers.
Previously I also had my system in my basement with a low ceiling and it always sounded best with smaller bookshelf speakers that were low to the ground as opposed to floor standing speakers.