Vincent,  Heavy touch weight is a "common illness" of Duo-Arts in
general, including Steinways, but it is not an inherent design problem.

It is a common myth that the longer keys of the Duo-Art (because of
the longer case and spoolbox) are a cause of the heavy action, but
this is simply not the case.  A properly rebuilt and regulated Duo-Art
Steinway OR or XR should feel as light and responsive as any similar
non-player grand.

Actually, in my opinion the longer keys actually can give it a slightly
better feel, since the key length is closer to that of a concert grand
Steinway D, with less leverage difference when played closer to the
fallboard.  You can see and hear me playing a recently restored XR
here:  http://www.youtube.com/watch?v=ewJEiuMJTxY 

My playing certainly isn't professional, but in my opinion, that XR --
and other Duo-Arts I've worked recently on, including an OR -- feel and
sound as good as any new Model M or O at the local Steinway dealership.
There are many possible reasons for the action to feel too heavy, with
most related to age, maintenance and improper repair and rebuilding.
Most Duo-Arts are around 90 years old, and none today are in pristine
original condition.

Many rebuilders of Duo-Arts today focus more on the player than on
the piano, or simply don't know to properly regulate and balance an
action.  And even experienced piano technicians, but especially those
who are less familiar with players, find it daunting even to remove
the Duo-Art action for routine adjustment and regulation.  So for many
Duo-Arts such maintenance rarely happens.  And Duo-Art owners are often
unwilling to pay a technician or a rebuilder for the extra hours it
takes to do the job correctly.  Or if they are willing to pay for it,
their technician may not know how to properly address the issues.

I've seen pianos showing signs of major redesign work such as
repositioned capstans or dramatically re-weighted keys, often done
in such a way as to make the problem worse.  The original design is
actually quite good.  When I rebuild a Duo-Art, I usually spend nearly
as many days on the repair, regulation and balancing of the piano
action for hand-playing as I spend on rebuilding the stack, pump, air
motor, expression controls and other pneumatic player components.

But investing the labor to get the piano itself right is the only way
it will play well, either by hand or with the player, since getting the
Duo-Art to consistently play quiet notes requires proper and even touch
weight.

First it is important to determine that the problem is actually that
the action is too heavy.  Friction problems making for a stiff or
sluggish action can arise from mis-aligned or warped action components,
dirty or corroded balance pins, front rail pins, dirty key bushings,
new key bushings that are too tight, worn knuckles, rubbing backchecks,
and center pin pivot friction in whippens, jacks, repetition levers,
damper levers, and hammer shank flanges.  Too much spring tension on
repetition levers or bass damper levers may also contribute.

Improper regulation, let-off and key dip, or even too-soft hammer
voicing can also make the piano feel "heavy" because it requires more
effort for a player to get the sound they expect.  I've even seen a
customer insist their grand action was too heavy when in reality it was
way too light (less than 30 grams down weight where 48 to 53 grams is
normal) which caused the action to feel sluggish because there was
insufficient up weight to quickly reset the action back to the proper
rest position when a note was released.

If the action is properly repaired and regulated, then a too-heavy or
uneven down weight is probably caused by too-heavy hammers or improper
key lever weighting.  As Robbie pointed out, new replacement hammers
are usually heavier than the originals, sometimes by as much as 2-5
grams, which with the action leverage can make the touch weight as much
as 10-30 grams too heavy, often unevenly from bass to treble.

When fitting new hammers, it is best to address this by removing excess
weight from the hammers before installing them, by tapering, coving,
tail-shaping, etc.  And then key lever weights usually still need to be
added, removed, or relocated to even out the action balance.  Again,
doing this right requires experience, skill, and is labor-intensive.
And unfortunately for some customers unwilling to pay for what can be
days or weeks of work, it is much easier to badmouth the Duo-Art itself
and say that it was "designed to play like a Mack truck".

Since I am unlikely to make it to Paris to evaluate your piano, I would
be happy to correspond privately to help you or your technician sort
through the issues, if you think it would help.

Best regards,
Ralph Nielsen
McLean, Virginia
http://www.historicpianos.com/