So here is my situation. I have a vinyl Gemini PT-2000 MK II turntable connected to an Allen & Heath Xone:62 Mixer which connected to a Line in on my Desktop.

I can record the records in Audacity. That is fine, however if I turn on the option to monitor the recording, audacity crashes.

I am looking for an alternative option to just listen to my records via my Desktop without having to record them and play them back. In other words I would like to listen to any audio going through my Line In input.

Here are my Desktop Specs
AMD Phenom 64-bit Quad Core 2.3 GHz
4GB RAM
500 GB HDD
Debian Lenny 64-bit

I am not sure what sound care it is. It is an on-board audio card that has SB as the Identifier and is running the Intel AD198x chipset. The Mobo is an Asus M3A32-MVP Deluxe. I use ALSA as well.

Anyone know of any software I can use to let me just Listen to audio coming in my line in without recording?

You should be able to just set alsa to pass line-in (or mic) through to your speakers, but there is the issue of RIAA equalization. If you don't pass it through an RIAA equalizer (either hardware or software), it'll be missing most of the lows and sound tinny. If your turntable has one built in, then you're good to go.

How do I set Alsa to pass line-in?

Bring up the alsa mixer (volume control) and look at the controls. In mine, there's a picture of a speaker under each input. If it has a red "X" on it, that input is muted. There is also a volume slider. Turn off the red "X" and increase the volume. Under Gnome it's Applications->Sound & Video->Volume Control.

I use KMix and I do have my line in un-muted and all the way up, However I do not get any playback.

I got it figured out. Kmix had Line In un-muted but had the IEC958 Playback source channel Hidden and it was muted by default. I just un-muted it and made sure it was set to PCM and all is glorious.

Cheers for your help Mate