All the DB means is that there is a Dolby FM De-emphasis circuit which was a short lived thing in the late '70s where some radio stations were using dolby encoding.....
It means absolutely nothing for the specs or operation of the unit otherwise....
Some units had the DB suffix after them some didn't, but they both had the Dolby FM circuit, as far as I can gather, Sansui may have trying to market the Dolby FM feature of those receivers......
It is not a full Dolby situation like the 9090DB for example, that has a dolby section which can be used with a Tape machine.......the 9000DB/901DB is not like that, and does not have any of the associated problems the dolby circuit does in the 9090DB.....