Bass and rubber surround ageing?
Regarding the speakers you mention (I have a pair) and I think that you'll find that the bass performance greatly depends upon how old they are. If you look at the bass unit surround, if it has a slightly milky 'mould' on the surface then it has chemically changed over the years. In consequence, the surround has hardened and the bass output has reduced. This may or may not suit your listening room! But if, as you say, you have been listening for many years, you will not have noticed this subtle acoustic change over the years. So, when you compare with the M40.1 you will immediately notice more bass because you have become accustomed - I suggest - to rather less bass.
Of course, your speakers may be from a different batch and/or may not have changed with time, but it's something that you should be aware of.
Alan A. Shaw
Harbeth Audio UK