Why did I suggest the way to add a foot pedals to a Duo-Art?  Simple:
because it's the way Aeolian did it, and it gives you a nice instrument
that plays Themodist rolls with all the possible expression you could
wish, and Duo-Art rolls as well.  That's not my opinion, but the
makers'.  The messenger is being shot at (what a surprise).

If you simply add foot pedals to an electric-only Duo-Art you will have
the spill valve open so you'll be pumping like the blazes to no effect.
That's the reason original Aeolian PEDA boxes isolate the theme side
when in manual mode, even if playing Duo-Art rolls.  Even if you
overcome that, the setup will require you to control the theme level
via the theme accordions rather than via the pedalled suction.  So you
haven't really achieved a foot-pedalled Pianola but a human-powered
Duo-Art.  Not much fun.

This is yet another case of "understand what you're doing first", if
you want to produce a nice instrument to use.  My posting was just to
point out the right way, as this sort of conversion clearly appeals and
if done wrong is deeply disappointing.

I have been told since my post that quite a number of electric-only
Duo-Arts in the UK come with the 6-pouch expression box, not just the
Weber instruments.  So, you know where to go to buy a piano that you
really can just add pedal exhausters to.

Julian Dyer