I second the subwoofer suggestion. I added one a couple of years back. The improvement seems to somehow go beyond the bass extension (my monitors are rated down to 40HZ). The sound seems more natural, more complete now. I may go for a more powerful amp next, but I'm glad I did the sub when I did.
Of course, as always, your system and your ears may not agree.
Of course, as always, your system and your ears may not agree.