I'm taking Spanish so personally I would choose that (that and the fact that I hate physics, haha) but I think you might find it difficult to catch up to everyone else in one summer - not underestimating you or anything, lol, I just think having a teacher is much easier.
To have a broad range of subjects I think maybe you should go for physics, as you have a language already.
Also, 6 A-levels seems pretty unnecessary, most universities only ask for 3 and an AS, although some people do 4 A-levels which gives you an advantage already so I think 6 is really adventurous - not to mention 3 As looks much better than 5 Bs and a C, which might happen if you overload with work.
(I'm only in year 11 but this is based on what other people have told me and what I've read looking into myself, haha, someone else might have a better answer.)