There is an article in the DIY section written by WingAdmin that you could use to get to the speakers. Here is the link to get you to the article. http://www.goldwingdocs.com/forum/viewtopic.php?f=14&t=10998 Just follow it until you get the dash panel off and you should be able to replace your speakers.
I have replaced my two from speakers and I set aside a day to do this which it can easily be done, just take your time.
While fitting new speakers I also managed to find a small set of tweeters to fit in the front. So my Wing now has 4 speakers at the front instead of just two. I have a 1988 1500/6.
If you look at the speaker screen you will see the large speaker and next to that you will see a small round speaker hole.
When you remove all the bits and bobs and get to the actual speakers themselves and take them out you will see some wires that are not fitted to anything, from what I have been able to work out is that Honda were going to fit tweeters but never got round to it or it may have been left up to us to do ........ you know Gold Wing riders, always wanting to do something extra to the bike.
As far as the speakers go I would recommend that rather than fit the honda speakers go to a boat shop and get the same size (fitting) and ohms. The boat speakers are water proof whereas the bike ones are not.