While I don't know your board but, I have never seen any parameter settings for line in on a motherboard before. Next time you see your buddy tell him it was the flatuator setting. What little I know about line in is not the mic in, but on rear of board. Generally these ports are configured within the software provided by manufacturer. It may be realtek which is common and can be found on cd provided by asus as well as documentation. There is some manipulation available.
Thank you roonj! I thought the suggestion was not valid at the time. Regarding RealTek, their support is totally useless. The support is obviously outsourced as the English (that is being kind!) is golbeldegook and of course not understandable-at least not be me. I have found a way around the problem, albeit unorthadox. I inserted a headphone stereo volume control in the line and conducted various tests with different genres and different input levels set by the volume control. A happy medium was obtained - at least for now.
This is weird, as I never before experience a "low level line-in" input. I thought there might be the possibility of the cassette deck line-out signal level being faulty. So, I tried another deck with the same results.
Thanks again for your reply and input.