I'm not familiar with subwoofers and would appreciate advice on
creating
a shortlist to audition.

My suspicion is that it is difficult to gain a lot from auditions
outside your room because an unequalized subwoofer is going to be
dominated by driving the room modes. If your main motivation was to
gain some bass oomph that might be fine but an attempt at accuracy is
going to be a lot more challenging.

A couple of suggestions: ask for a demonstration in a modest sized room
of the difference between a simple passive subwoofer and one that tries
to compensate for driving the room modes. Alternatively, compare the
passive subwoofer against a good pair of headphones. This may not tell
you what will happen in your own room but it should give some feel for
what is missing without a subwoofer and whether a passive subwoofer
(with large deviations due to room modes) is going to provide an
acceptable improvement or just add a bit oompth and sound a bit weird.