Question on AP Requirements from American applicant

Hello,

I'm an american student studying at a US boarding school. The boarding school that I attend is quite well known and unfortunately does not teach classes according to the AP curriculum. The rigor of courses is quite high, so because of this, not many students in my school sit for the AP exams.

I see that the Oxford requirements for US students lists:

https://www.ox.ac.uk/admissions/undergraduate/international-students/international-qualifications?wssl=1

USA Oxford will accept both the old-system and the redesigned SAT for entry in 2017 (or deferred entry in 2018). Students sitting the redesigned SAT will need to achieve a total score of 1,470 (out of 1,600). We do not require the optional essay in the redesigned SAT. Any candidates with a test date prior to, or including, January 2016 will be expected to achieve the SAT Reasoning Test with at least 1,400 in Critical Reading and Mathematics and also 700 or more in Writing, giving a combined score of at least 2,100 (out of 2,400). OR ACT with a score of at least 32 out of 36 AND Grade 5 in three or more Advanced Placement Tests in appropriate subjects OR SAT Subject Tests in three appropriate subjects at 700 or better. A combination of APTs and SAT Subject Tests (or other equivalent qualifications) is also acceptable, if they are in different subjects. Individual courses may have specific requirements, so please check the course pages for details.

I'm interested in applying for Oxford, but I'm wondering how they would handle a college level classes taken during high school? In particular I took a calculus class at my local state university over the summer and received the highest grade possible "A". Would it be possible to substitute this grade in lieu of one of the AP exams?

Does anyone have any experience with this?

Many thanks