I notice that the original caps are all non-polarised electros. While
changing to film type caps (Mylar MKT or polypropylene MKP)

Polypropylene is probably overkill.


is thought by many to improve the sound quality, this may prove
to be a moot point. Those 24 uF and 40uF caps will take several
paralleled MKT's or MKP's to get the right value and the cost
won't be all that small.

Mylar caps aren't horribly expensive.

I would start by replacing only those caps in series with the drivers -- the
4uF and 24uF capacitors. You can then try replacing the two that are
directly in parallel, the 8uF and 40uF. The 100uF cap seems to be part of a
Zobel filter (don't ask) and probably doesn't need replacing, unless it's
"bad", in which case you can use an electrolytic.


As suggested by William, you might care to modify one unit
and compare it with a standard x-over. A listening test will
require a suitable speaker switchover arrangement.

Not necessarily. Before modifying a speaker, listen to a mono source and try
to get a sharp central image. Modify one speaker, and repeat the listening.
If the caps have changed the sound, the mono image should be at least
"different", and (hopefully) degraded, because the speakers no longer "sound
alike".