The first one (1(a)) is incorrect. The second one (1(b)) is correct. It's the position of the correlative conjunctions that makes the difference. The first one would be correct if it were written something like this: "I not only love American music, but I also play American music." In the second sentence, the verb precedes the correlative conjunction and thus applies to both clauses.1.(a) I 'not only' love American music 'but also' American art.
(b) I love 'not only' American music 'but also' American art.
Neither sentence is correct. Try: "I have travelled not only all over the US but also all over Canada." Or: "Not only have I travelled all over the US, but I have also been to Canada."2.(a) I have 'not only' travelled all over the US 'but also' Canada.
(b) I have travelled 'not only' all over the US 'but also' Canada.
Neither sentence is correct. Try: "They're not only planning to visit England, but they're also planning to visit France."3.(a) They're 'not only' planning to visit England 'but also' France.
(b) They're planning 'not only' to visit England'but also' France.