Hi. This question may sound stupid, but is the E-string of a 4 string bass supposed to naturally sound duller (less sustain) than the other strings (especially the D and A)? This question applies to any bass.
they shouldn't. They usually only sound duller because it's the one you play more. More oils and dirt get on that string than any other.
The string could sound duller if the string tension is too loose. Does the A or D string feel tighter when you play compared to the E string? Are you tuning down or using Dropped D tuning? A tight string usually puts out better harmonics than a loose string. To see if this is the case, take one of the strings that is bright (like your D string) and tune it down 2 steps - it most likely will sound duller. It also may have something to do with the string height. Check to see if the E string is farther from the pickups than the other strings - this could affect how the harmonics are picked up. Many companies make taperer wound strinds that help in this area - strings don't have as much mass at the bridge and are not as high. Some claim that Tapered strings provide better tone, tension and sustain. I have used DM SR-2000 on several basses in the past and have found that the strings have good string tension and tone.