Another question is the difference between LM1875 and LM1876, is it really LM1876=LM1875*2?

LM1876 is not equal to LM1875*2, because the sound played by the two is quite different. LM1875 is bold and unrestrained, while LM1876 is pure and pure. The static current of LM1875 is larger, while the static current of LM1876 is smaller.