Any comments appreciated,

I had exactly the same problem with my KEF 104's. Eventually I tracked
it down to a blown tweeter in the left speaker. Amazingly, the tweeter
adds very little audible stuff, other than the "ambience". I'm planning
to purchase an old stethoscope to simplify diagnosis of this problem in
future.

Then I had the same problem again only last week with a pair of Rogers
LS1's that I'm connecting up to an old QUAD 33/303 for our holiday home.
In the end I deduced that the volume control had gone seriously
one-sided during years of being stored in the attic. Whizzing it up and
down a bit fixed that, fortunately.

My first test was to swap the speakers left to right (so the left sound
came out of the right and vice-versa). This was to eliminate problems in
my ears/perception. I'm getting older, and get wax in my ears, so I had
to eliminate the probable cause first.

--
Steve Swift
http://www.swiftys.org.uk/swifty.html
http://www.ringers.org.uk