Audio Note speakers are ideally located near the corners of the room; if not in the corners, at least close to the back wall. In a room of this size, and the kind of music you favor, you may actually have options to use speakers that are not quite as efficient, which greatly increases your options, particularly if you don’t insist on a SET. That said, a SET amp may still be a good option if you are willing to accept that they will not be at their best at head banging levels. To me, the great attributes of such amps are best heard with relatively high efficiency speakers and I don’t know of many that I like that are not somewhat pricey. Do you have any idea of how much you are willing to spend and will you consider used speakers?
I don’t agree that Harbeths are out if you go with modest powered tube amps that are not SETs. I particularly like the Harbeth 30.2 with tube amps of at least 20 watts. You can find reasonably priced EL84 amps that sound very good that are reasonably priced.