you did not mention which type of speakers you are driving.
the 555 can sound bright on some; benefits greatly from parts upgrades. The 555 Mk2 has a bigger power supply than the original, but still small when compared to the Bryston.
The bryston will give you more bottom end control. A more fair comparison to the Bryston would be the Parasound 2200 Mk2. The Adcom while at its price point is OK, is not in the same league as the Bryston or Parasound 2200 Mk2.