HARBETH: Amplifier for classical music & HL5+ ?

First of all, sorry for my poor English. I am a very happy new owner of the Harbeth Super HL Plus. To complete my listening chain I wanted to ask you some questions about possible amplifiers that can be coupled with these superb speakers. I'm a fan of classical music and my listening ranges from the Renaissance polyphony to the great Mahlerian symphonies. The source of my music is largely in high definition format. I have a fairly large room (4.5mL x 7mD x 3.5H) with distant speakers about 6.5m. I can listen to music at appropriate volumes, basically as in a concert hall. Starting from these parameters what integrated amplifier could you suggest to me? At the moment I have a Cambridge Audio 840a. With a Supernait2 or a Sugden A21SE or an Electrocompaniet ECI5, just to make some examples, could I improve my music scene? Thanks for your input.