>>Most records drive the soundcard to clipping.
First, unless you want to digitize vinyl, why are you feeding the Cornet2 directly into your M-Audio sound card? For listening, always feed it to a preamp or headphone amp because the phone out of the sound card sounds average at best and will dumb down the performance of your phono setup.
For digitizing vinyl I'm experiencing the same clipping issue with my new M-Audio Firewire Audiophile sound card feeding from my switchbox's rec-out (virtually a direct feed from the Cornet2). I'm surprised that it has no input level adjustment of any kind.
>>I'd like to avoid putting anything additional in the signal path from Cornet to soundcard.
Attenuation is job for the preamp. Adding to the path is unavoidable unless you wish to modify the gain of the Cornet2 (not something I wish to endeavor).
For my setup, I'm adding a volume knob to the rec-out path of my switchbox to attenuate the input level to my sound card.