So sorry about the late response. Our team was away during the Holidays through New Years and we are now catching up with all your requests.
Unfortunately, we do not currently have a built-in solution for Line Input. However, multiple users in these forums have created their own solutions for their specific setups. You can find many of them by searching for Line In in our topics view of the forums. Here is an especially detailed one on the use of the Cirrus Logic Card for Line Input: https://www.max2play.com/en/forums/topic/using-multiple-inputs-with-max2play-on-rpi2cirruslogic-sound-card-independently/