Your "surmise" is wrong.
I believe that I'm correct in saying that windows picks up the sound output from the devices from the ide cables, and not the audio cables as per linux.
You will probably have to open the box and see - I can get sound from both my cdrw and dvd drives under windows, but when in linux, only the cdrw, cos that's the drive with the audio cable from the drive to the sound card.
If you open your box, you could check to see if there is facility for your sound device (card/chip/whatever) to have multiple (well at least 2) connections from drives (like a total idiot, I forgot to check last time I had my box open), if so then you should be able to just plug the second device in and "off you go".
Failing that, I understand that the very latest version of XMMS (1.2.8 I think) has the ability to pick up output from devices digitally (as opposed to analogue i.e. no audio connection made) but you would have to check this out it's got something to do with /dev/dsp and no, I have only read about this, not tried it yet