How do I make mp3's sound good on my car stereo

I just bought a nice headunit for my car that plays Ipods and thumb drives so I used frostwire to download music and then used NCH to try different bitrates. 256-constant sounds okay for some songs but others sound like crap. So I tried 256-320 variable bitrate and the songs that sounded like crap still sound like crap and the ones that list at 320 kbs sound unnantural or too precise. I thought 320 would be better but sounds really odd to me. Any suggestions? Ive heard some people say that the original encoding has to be high quality. I wanted to start buy music online from Rhapsody but I don’t want to if the I can’t make the sound somewhat close to that of cd’s.

Ive heard some people say that the original encoding has to be high quality.

Welcome to the forum. You have indeed heard right. Increasing the bitrate of a crappy file isn’t going to make it any better. And when you do encode, LAME is probably the best (free) encoder out there.

If you want the highest quality MP3’s then buy the CD and convert, when you buy(hopefully) MP3’s online you don’t know what you’re getting until you download it. Windows Media Player and CDex do a good job converting, WMP uses the Fraunhofer codec.
TIP: some players prefer CBR over VBR.

I use both Amazon and iTunes for downloading music, and the quality is very good(to my ears)…As stated, you never know what krap you’ll get from the OTHER sources…You really do get what you pay for(or not)…
And of course, nothing substitutes ripping/converting yourself…