Everyone stressing the importance of using the Bose dedicated EQ is right on. I bought a used pair years ago which came with the EQ. Since I already had a very good 10 band EQ I thought it would be better than the Bose. Like you say...They sounded "flat".
I also read that the speaker foam surrounds deteriorate with age and, upon removing the grills, found that was the case. Bought a kit and replaced the surrounds. Still no improvement. For the heck of it I hooked up the Bose EQ. Sound was much better but still "flat". The speakers just don't match up to a lot of others for much less that the cost of the 901's.