can someone please tell me the settings to copy normal audio cd on the fly and why there is always a buffer underrun
thanks

There's almost always a buffer underrun because drives (CD-RW/CD-ROM/DVD-ROM) read audio slower than data (they cannot deliver audio as fast as they can deliver data and therefore a buffer underrun is the result).

There are no options in CloneCD to speed up the audio reading. The only thing you can try is reducing the write speed.

Or buy another reader...
There's a lot of difference between different brands of readers on how fast they can read audio CDs. I have a Toshiba which is very slow indeed (around 7/8x I believe). Other drives happily do DAE at 30x speed or so. But anyway, buffer underruns aren't that big a problem anymore since burnproof and the likes have been around. I you really wanna do on-the-fly copies, buy yourself a drive which supports burnproof/justlink/seamless link, it's worth it.