It makes no difference whether I change the playback or recording levels for Line-In; the peaks still stay the same.

This is really starting to annoy me because this song that I have on cassette sounds perfectly fine but keeps getting oversampled and having the bass ruined because of the too-high peak levels whenever I record it through Line-in.

If this problem can't be solved, then I'll have to settle with AIPL Singulator to do my line-in recording and use AG only for CD's :P