I’ve owned all these amps except the Ayre, which I had the non-20 version on demo years ago. They are all quite different sonically. I like the Luxman quite a bit as its musical, transparent, with great texture- but its a top down amp so if bass is your thing, then I’d look at other options. It also is limited power wise and might require monos on inefficient speakers.
The Rowland has better bass, and very rich almost creamy midrange. If female vocals are your thing, this is the solution. It works better on speakers that are more neutral/cool. I liked it quite a bit.
The Ayre is very even sounding top to bottom, with super natural sounding treble extension. But its flatter dimensionally than the rest. Its as if 3d images are on a 2d plane. I’ve heard the 20 series is more dimensional.
Finally, the Pass is probably my least favorite. It’s warm, but not very musical in that it has way too much leading edge, thin timbre, and is flattish. I also found it not as powerful sounding as the specs claim and soundstage was more in between the speakers. The bass is a good point but its a bit round which some may not like (I do).
If you want an inexpensive set of monos that delivers, try out a used pair of Ampzillas. They are competitive with all of these. I also love the DarTZeel 108 which used is excellent value on relatively efficient speakers.