Boesendorfer grands have 96 keys, adding the extra to the bass section.
I have never run across music that required the extra keys, but there
must be some.

As to the tonality of the bass, there are two factors, one is the
string length -- at 9 feet, this is not a problem on the Boesendorfer
-- and the other is string 'cohesion'.  This means that as a wound
string ages, its copper wrapping loosens and the tone falls off
dramatically.

This can be somewhat cured by loosening the string, lifting the loop
off the hitch pin and giving it a twist in the direction of the
wrapping.  This can bring back much of the tone, but the ideal is
replacement of the bass strings (a full set costs around $100).

Jason Stahl