Forgot to mention:

It may be possible to do a basic course on a part-time basis so, you would still be able to work full time and perhaps do the sound course at night / on weekends or partially by correspondence.

Check out your options.

The UK's Open University's actually a very good place to try. www.open.ac.uk
They're a fully recognised, highly respected distance learning university and offer a range of technology courses that you can do while working and from outside the UK and Rep. of Ireland where the Open University primarily operates.

They certainly have some courses that could be used to lead into a sound engineering or other media career.