Michelle, just convert the ACC songs on your iTunes to MP3 and burn them as CD Audio files (not MP3) because I don't think you can play MP3 in your X5. There are 2 options you need to check for in iTunes. There are under the Edit > Preferences menu:

1. Under Advanced tab, click on Importing tab, and select MP3 Encoder
2. Under Advanced tab, click on Burning tab, and select Audio CD

Then just select your ACC songs, right click and select "Convert selection to MP3" option, and drag the MP3 version of those songs to a playlist, then click on the round circle at the upper right corner to burn them to a CD

Good luck!