My recollection was that Horowitz was famous for only using his only piano for concerts. Googling for that I came across
http://www.bruceduffie.com/mohr.html which is a real gem for those interested in all matters relating to the art of the piano technician (and copious references to 'the Horowitz piano' therein).
Bert, no comment from me on the samples you posted as I've not had a chance to listen to them yet.