Moving to seperate components brings up a whole other world......dollar wise. Get your system set up as is and then decide on that external amp, you may find the system is just fine.
I am still waiting to get a seperate amp and am constantly searching for reviews of cheaper/older ones available and in the used market. Unfortunately I have no idea how much better they will sound, if at all.
I do know that I really liked the way my system sounded with the A1400