welcome to Amiga.org, RMC64. :-)
I'd try plugging the Amiga into a stereo with an AUX input, to make sure the Amiga is outputting sound properly. The configuration you've described should be working. I used to use a Y split with my 1084 (not stereo model).
In hindsight, it would probably be better to use a gated Y joint than a simple Y splitter. This would remove the possibility of shorting your left channel into your right one. ;-) I, personally, don't know of anyone who ever damaged an Amiga by this, though, so I'd think it unlikely to happen.