People come in asking for us to build them brand new gaming computers all the time, but nobody ever suggests they get a sound card unless they specifically ask about it.
We push out plenty of $2000 systems without any sound cards at all.
Yes the sound would be better with a dedicated card, but you would probably have to have a pretty discerning ear to tell the difference.
Having one, however, does bring with it some baggage. For one if you don't have a sound card it can't disrupt airflow nor can it generate increased heat over what is already built in.
Most of the time the sound card would be below the video card since PCIE-1 is usually the one highest on the board, that means the sound card would be between the video card fan and the air the fan wants to suck in.
I would try it without a sound card and if you feel the experience is somehow lacking then think about getting one.