In general there are facilitating subjects: Maths, Further Maths, the Sciences, Languages, English Literature, History, Geography, etc., which are generally preferred by top universities - some of which actually publish the list of the ones they consider as such. Their general advice is to have at least two facilitating subjects. If you think you will prefer Music Technology over Music then take that, it's not about having all facilitating subjects, but at least two generally makes a strong application for top universities*. For many, perhaps even the majority of universities, your application will be fine as long as you meet the entry requirements, and the subject is usually not important**.
*There are some exceptions to this, particularly Science courses, where having three or four STEM subjects is generally considered standard for a competitive application at top universities; as well as for Oxbridge, for which most applicants will have mostly facilitating subjects.
**Any subjects that are required for your course will obviously have to be taken, and even if there are no specific requirements, it would be beneficial to have a subject that generally links with the subject area of the degree, for example an Arts subject for an Arts course. Also General Studies is usually not accepted, though this is no longer offered.