I haven't listened to your speakers but they may not be the best for soundstage. If I was in your shoes, I'd consider that. Try to borrow some more conventional 3 way speakers with an exceptional midrange. Midrange is where the soundstage exists. Not sure how horns affect soundstage. Some others with horn speakers may chime in but I would wonder if the horn design is affecting soundstage.
Agree with speaker placement.
Also, for soundstage, I think your best results come with the minimalist approach. The less times the signal is touched by the system the better your soundstage will be. Pass is a good amp but ss amps always do a lot more to the signal.
Jerry