A Studiomix is not a finished product yet. To create a song that sounds the same on every medium, be it radio, youtube, TV, CD,Vinyl... it needs to be mastered well. Mastering is the last important stage in the recording process and it takes a lot of experience and skill to deliver a perfectly mastered song/album.
We have no in-house mastering engineer but we can suggest some mastering studio's/facilities/engineers who can deliver top-notch work.