Congratulations on finding a _working_ Orchestrelle.  Too many of these
fine instruments stand mute in collections because of the tremendous
amount of work required to restore them.

My informed guess on your keyboard ciphering problem is this:
I suspect that on an Orchestrelle, unlike a regular reed organ, the
manual keys do not press directly on valves.  Instead, they each open
a small valve which leads to the inner pouch boards, just like a
tracker bar hole.  The selector knob controls whether the pouches are
driven from the roll tracker or the keyboard.

If so, then your low E key has a faulty valve under it -- probably a
small patch of leather has come loose.  That should be easy to fix.
Worse, there could be a problem in the changeover switch between the
tracker bar and the keyboard.  That switch may be a big long slider
full of holes, or it may be a set of pouch-leather logic gates which
work exactly like modern CMOS electronic computer gates.  Releathering
that would be a job.

I'm speculating form my knowledge of tubular pneumatic pipe organ
actions, which worked as described above, using a lot of player piano
technology plus the "CMOS" gate arrays to handle the couplers between
keyboards.  Tubular pneumatic action was very popular right around
1900, during the transition between tracker and electro-pneumatic
actions.  Likewise the "ventil windchest" on which the Orchestrelle is
based.

In many ways the Orchestrelle is a pipe organ with reeds, stood on end!

As for the "Golian" stops -- a large fraction of the pipe organs in
the USA were built by the M. P. Moller company (alas, a recent victim
of Perflex and other things).  Their florid Danish-German nameplate
on their consoles led to quite a few letters' being addressed to
"H. P. Holler."

Best wishes, Mike Knudsen