Agree with @ryder on the statement of the integrated. Many times, using an AVR as a 2ch preamp is not an optimal solution, and you won't get the best performance out of a better 2ch separate amp. It may be better to have a high quality integrated amp with a good preamp stage built in and home theater bypass so the analog signal is completely processed by the integrated vs the AVR.
Moving to separates
Does anyone have an experience they'd like to share about going from just an AVR or integrated to using external amp(s)? My Integra AVR has 100 W per channel (class AB), all channels driven, and sounds very good, so it is not clear to me that there is any advantage to connecting its preouts to a separate amp. Might be a total waste of money. Please mention your specific equipment. Thanks!