Ok your motherboard has onboard sound, as ASUS have some audio drivers available for it on their site.
Usually if a seperate pci sound card is fitted then its best to disable the onboard sound in the bios.
Anyway if it is or it isnt disabled you need to make sure you know which input you are connecting to.
If its in one of the horizontal slots below where the pc monitor connects to then that will be your soundblaster live card.
If it plugs in higher up the tower, near where the mouse and keyboard and USB ports are, then you are using the onboard input.
In the program that you are using to record the LPs from there should be an option for the "audio input source".
It may be under a section called Preferences, Properties or Initial Setup, or something like that.
It should give you the option to select the soundblaster live or the name of the onboard one.
If it only mentions the one device then plug your line out from the record deck into that input, that was the case with my video audio problem that I mentioned earlier.
Again I havent used those particular programs so I dont know the exact section that you need to look in.
I dont think that you would damage anything by using the Mic in port, although it may distort the sound if the levels too high.