Hey Abancke,
What sort of outputs does your laptop have? I connect my macbook pro to both my onkyo 805 and my pioneer sx-1050 via 3.5mm headphone to L/R RCA cables. I have just made sure to put them into a NON-amplified input (CD input for onkyo). The sound is good, not great. I can tell the difference between a CD playing on my oppo DVD player and playing through my computer. It's not so much the cables as my Oppo is connected to the pioneer through RCA's (it's 30 years old so no HDMI) and the onkyo through HDMI. I prefer the sound from the older pioneer from the CD player when I do A/Bing on the amps with stereo 5T's. I think it's more an artifact of how I've burned the CD's or how the laptop outputs the sound. Even though I burn CD's on the Cd quality setting something gets lost although it may be the laptops output (itunes has an output equalizer that you should play with). With the onkyo I've found it changes a lot depending on iTunes equalizer (i.e. jazz, concert...etc). I think if you can live with "good" sound it's absolutely fine to use the headphone to RCA cable. If you want the best sound you'll have to use a CD. I know some people have had some success with wireless (i.e. using an airport express) to connect to the receiver but I'm happy rolling out my extension wire to listen to some music when I don't want to shuffle the CD's constantly.
Hope that helps!
Jason
Speakers: Aperion 6T's, 6C, 4B's, and 8D
Receivers: Onkyo 805 and Pioneer SX-1050
DVD player: Oppo 981HD
TT: Pioneer PL-71
Amp Selector: Niles DPS-1