I think the DB2 was a 2 hands only manual watch, whereas the DB5 was self-winding and had a center seconds hand.
On the same Watchbox page I also found this:
DB1 – Monopusher chronograph with center chronograph seconds register and 30 minute register
DB2 – A simple time-only watch with no seconds hand
DB3 – GMT with power reserve indication, with 7 day power reserve
DB4 – Minute repeater
DB5 – Time only with center seconds
And here's an in-depth presentation of the DB5: watchpics.com

DB2

DB2

DB2

DB5

DB5