For what it is worth: a couple years back I talked to the widow of
Wolfgang Pauli (another Nobel-prize winning physisict) about this.  She
said that she had heardEinstein often and always thought that while he
was technically an accomplished amateur, able to play all the usual string
quartet literature, his tone and his feeling for rhythm were not on par
with this, to the degree that listening to him play never gave her
pleasure.

Regards, Andreas