Well, here's the "special one".
Rienzi's rehearsals has been published,
but I don't know if the CD is still available;
anyway this alternative source is very good.
Beethoven's First Symphony was released
only on old LPs now unobtainable (MDP and ATS),
but never on commercial CDs, if I'm not wrong.
I had the LP MDP 037 many years ago on loan
from a collector to make a digital copy of it.
The conversation was captured in Milan (1954).
I've included in the folder an english translation.
Mitropoulos, Cantelli's close friend,
performed Strauss's tone poem in his memory,
a few days after the plane crash.
Among the many testimonials of their friendship,
one is very nice (reported by Cantelli himself).
After a performance of Berg's Wozzeck at La Scala,
Mitropoulos was invited
to Cantelli's little apartment in Milan to have dinner.
Then Dimitri went to the piano, playing,
explaining and singing loudly Wozzeck until late at night.
At one point the protests of the neighbors arose
and forced them to quit
(may the gods forgive them).
FLAC - Details, translation and some photos included.