iMac DV+ and sound problems

[zero10]

I have finally able to get Xine to build and run on my iMac DV+ running YDL 4.0.1, I am presently working on getting xmms to work, and I am confident I can do that, however I have a more basic problem.

The iMac is in the front room of my house, so it's just a little e-mail checker and whever else anybody wants to use it for computer. All of my good computers are located elsewhere.
However, I have always wanted to be able to listen to the wrif ( www.wrif.com ) on this computer, and consequently on my stereo in my front room (much better speakers). So, I have finally gotten it so I can listen to the MP3 stream, however I only have one volume settiing, loud. I can fiddle with all of the volume controls that I can find, and they don't change anything unless I turn them right off, at which point it is muted.
This in itself isn't a big deal because I wish to connect it to my stereo, however what is a problem, is that I cannot find any way to turn the speakers off, and to turn the line out on the side on!
If I use the headphone plugs on the front, they are very very quiet, and the speakers are still playing very loudly.

If I go into the volume control, it tells me I have a powermac screamer sound card, which judging from what it is doing is a very accurate description, but my hunch is that it has mis-detected my sound card. Any advice?