Any SET amplifier you buy should have adjustable negative feedback as that greatly helps in getting the best sound out of different speakers.
I am really over SETs that have fixed zero negative feedback.And many of the most expensive ones are like that.They tend just to be a fixed tone control.
I owned an Almarro 318B that was very well balanced sounding SET and could drive many mainstream speakers.It had a moderate amount of negative feedback to assist in that regard.I had a variable negative feedback control installed and that really helped on certain speakers.I mostly preferred it with a bit less feedback but never with zero.