I did put magnets under the pickups on my Ursa 6 along with changing the strings to GHS flats. Big difference in tone and output. Volume now on par with most other passive basses I own and the tone is much more detailed and present. Quick and inexpensive upgrade.
the magnets I have are 2mmx4mm and the A string is really the only weak one. what do you suggest? My output ain't so bad. In a live setting somewhat loud I can tell that they're not great pickups. So I'm thinking magnets all across the entire bottom of the pickups and maybe a few extra under the A string.