Small room, long wall placement. I would look for a used paid of Larsen 6/8/9s. These are designed to be placed on the long wall, directly against the wall. These will paint a huge mural of sound on the wall behind them, and there is essentially no sweet spot. Stunning and your Pass Labs amp will work just fine, at least with the 6/8s. Unfortunately they went out of production when John Larsen passed away a few years ago.
My second choice would be a pair of Audio Note speakers, K, J or E. I'm very fond of the K and J speakers in smaller rooms. Although they are designed for corner placement they will sound great right against the wall. I'm using a pair of AN Js right now in a room approx. the same size, although on the short wall. These will also work very well with your Pass amp.
My third choice would be for a pair of JBL studio monitors with B-radial or CD horns. Maybe the 4425 or the more user friendly home version, the L200T3 (if you can find a pair). These need a scootch of room behind them but not much. The horns are very wide dispersion so the sound is pretty even across the width of the room.

