I'm currently running my PC through an older JVC mp3 player deck with no issues.
All I did was buy one of these...
(eBay is the best spot for this....picked mine up for 20 bucks)
...then plugged it into my sound card's "line out" jack using one of these:
(NOTE: If you can't find one of those puppies that is long enough, you can easily use one of these adapters, along with a standard Male/Male RCA stereo cable:
To make the sound go through, all you have to do is select "CD-CHG" on your JVC deck and it'll use the CD-Changer input as the source. That's the way mine has been working, and I haven't had any issues so far. Much cheaper to use an old deck that was lying around the house than buy a new amp or something.
Hope this helps.