Welcome Martin.
Onboard sound vs. soundcards - I believe this is a question of evolving history. The original on-board sound from some years ago used to be greatly inferior to having a dedicated sound card. Depending on your exact purposes and functionality needed, that gap is always being closed. I think today it is to the point where basic stereo (or surround even) playback likely doesn't need a dedicated sound card as long as you have good flat response, low THD on-board sound. However if you want to get into REW and other advanced uses then a dedicated card can definitely be worth it. Carefully evaluating the OB sound versus an add-on card for your specific purposes I think will give you your answer.
