I might be able to help. I was an armor officer for 21 years, twelve on tanks. I started on M1A1s 1987 and ended in M1A1 HC in 1996 as a company commander. Those tanks are very similar, the HCs had DU armor. We did not have an active misled defensive system in the HCs. Both tanks had equals armor and protection from heat rounds. DU provided improved protection from kinetic/penetrators for the HCS. It doesn’t stop all rounds, it does shatter some rounds and forces bounces on others. On either tank HE rounds are ineffective. HESH rounds are also in affective due to the thickness. The M1A2 were HC with a hunter killer system for the commander, better communication systems. All three carried DU rounds for 70 % of their ammo (we hunted tanks. We believed at the time, USSR tanks carried very few sabot but lots of HE and HEAT. The hunter infantry. The time to upgrade to the AIM probably included a full rebuild and the removal of the DU. Egypt and Saudi and others also use M1A1 now. I also trained on the M1, M1ip and M60A3 TTS if you have questions.
Update?