Is there a way to go from PC to receiver/MP3 play?

Easy. MP3 quality is crap anyways, so just mosey on down to the Rat Shack and get an 1/8 mini-plug to RCA adapter. Also buy an 1/8 headphone extention cable. Plug the extension cable into the back of your soundcard, and the adapter into the extention cord. Easy!

The more complicated (and expensive) way is to use the onboard DAC of your receiver (assuming that you have an empty digital input). If your soundcard has TosLink compatible outputs, just run that into the digital input of your receiver. The drawback to this is that mostly likely (depending on your software and soundcard) you'll have to convert the MP3's to WAV format before playing them. Cheers!

I run the digital output of my soundcard into the digital input of my phillips 880 cdr, then into a receiver via the phillips analog out. It's a little jittery, but fine.
Beware that your PC can output some gawdawful LOUD and high pitched sounds without your prior approval. I was going to hook up to my high end system, but decided it was a bad idea for this reason.
A cheaper way would be to buy a 1/4 jack to rca adapter at radio shack (or headroom for a high quality one). Lastly, buy a soundcard with rca outputs.

I got a good deal on a sound blaster extigy a bit ago. I got it in favor of the audigy platinum due to lack of a free drive bay at the time. At first it had much worse sound than my old live card, but after a firmware upgrade, it sounds great, it has an ac3 passthrough, then you have you choice of toslink or digital coax out. The only problem is, if your receiver doesn't have a user defined crossover, you could find your sub not used for mp3s, in which case, the audigy and the extigy, have 6 channel analog out.

One thing to keep in mind, wish I would have known this before. You can use a mono-miniplug(1/8 inch) to rca connector, then some digital coax wire, to connect anything in the audigy 1, 2 and extigy series up to the coax in your reciever. And if you're feeling cheap, just get some rg6 cable and rca coax f connectors.