The P3ESR is much more than adequate to hear ANY improvements in the upstream components. It is surprising how well all of these speakers based on the BBC LS3/5A speakers sound and how much they appreciate good upstream components. I've heard, and liked, a number of Elekit amps. However, if you do push the P3ESR hard with such low powered amplification, you might run out of steam (the first sign would be compression -- the music stops getting louder and sounds more "blah"-- and the sound becoming more muddy. I am someone who believes most people grossly overestimate the amount of power they "need," but these speaker do need more power than most speakers; they are not as easy for tube amps to drive as some other BBC LS3/5A variants that have a 15 ohm impedance.
I don't know about the upgrade options. You should talk to Victor Kong, the North American importer. He is usually quite frank in his recommendations.