i think if you really want "raid boss" experience you might wanna try mods. i believe "creature level and loot control" makes bosses a 5* monsters. and it can also add few interesting modifiers: like twins - 2 bosses instead of 1 with shared hp pool. or summoner - calls adds from time to time. etc.
yes, it's not vanilla. but it makes process of killing same boss multiple time more interesting.