I routinely finish my acrylic/mixed media paintings in the following way to achieve a satin, encaustic like finish using cold wax medium as my final coat:
1) I use Liquitex Pouring Medium (or Golden Self Leveling Gel) to coat the entire surface of the painting while it is laying flat and is sitting on a level surface. This is important because if the surface is tilted or slanted, the pouring gel will move with gravity and you want it to distribute evenly over the surface of your painting. Apply the medium with a brush. Sometimes, you will need two coats if your surface is very textural and is not coated well with this medium, but in any case, let each layer dry completely before the next step (overnite is a good idea). *NOTE: Whether your painting is large or small, you can tilt the surface to help you distribute the pouring medium but it will obviously drip over the sides - if the work is small, you can hold it over a trash can, allowing the drips to be disposed of, OR, you can place paper underneath to protect your surface and you can use a brush to even off the medium along the sides, so it is coated as well. I will typically elevate the work on some wooden blocks so excess medium can just drip off the edges/sides - and I wipe the edges smooth and evenly while still wet. NOTE: If you have used ANY water soluble dry mark making mediums, make sure you apply a very small amount of acrylic polymer gel medium with a paper towel right over the mark to prevent it from smearing when you apply the pouring medium or Golden Self Leveling Gel. You can also use a light coat of permanent spray fixative.
2) Next, once this layer is dry, you will see a very high gloss finish. This should be very smooth and have covered the surface evenly, but if not, you can brush on more of the pouring gel to fill in any recessed areas or areas that might have been missed; again, let these areas dry thoroughly.
3) Take steel wool, "0000" (the finest grade of steel wool) and dip it in water. Use a circular motion over the entire surface, keep the surface a little wet as you go. You are dulling the surface so it will go from high gloss to matte finish. Once you have done a thorough job, wipe the surface with damp, clean paper towels to remove any residue/steel wool bits from the surface. Move to step 4.
4) Now, take a clean blue shop towel or paper towel, etc, and apply a thin layer of cold wax medium over the entire surface, including the sides (I happen to use Gamblin Cold Wax Medium but any Cold Wax Medium should work). Again, with a circular motion, rub the CWM over the entire surface of the painting, wiping off any thick areas or excess. Let this dry thoroughly - 20 minutes is usually enough but I typically let it sit a few hours.
5) Buff with a nice clean cotton cloth. The shine will be a satin finish much like that of an encaustic work.