I got a headache trying to follow your last post.
Unless you can provide more of a description of what that "a/v out (svideo looking one)" does, you might be stuck with what sound that monitor can deliver. If we knew what it does, maybe we cound help more. If it is, in fact, just an S-video out then you're boned.
An audio in is just that, an input, not an output.
Now, you might get by using that orange digital out on the TV box if you're willing to spring for a relatively inexpensive external DAC (Digital to Analog Converter) to convert the digital audio into analog so you could drive those speakers. Naturally, you would have to control the volume with the speakers volume control.
If you're open to that last idea, chime in. Others will pick up this thread I'm sure. As to which one (there are several types), I'll leave that to the more technically inclined.