A lot of people are having overheating issues with Ensoniq samplers (both racks and keyboards). That’s because of the way they were built. The lid acts literally as a heatsink to evacuate the heat building inside (because of the power supply). All you need to do is make sure it has airflow all around the unit, especially underneath it (where it heats the most). If you have a keyboard, don’t put it flat on a table because heat will build inside the unit with no way to evacuate, causing instability and other issues. Use a keyboard stand so airflow is cooling the base of the unit. If you don’t want to use a stand, be creative. Find a way to leave a gap between the table and the keyboard, especially under where the power supply is inside the unit. It’s the same thing for the rack version. Whether you keep it racked or on your desk, make sure there is airflow underneath it, let it breath! You’ll never have overheating issues this way. Any electronic gear, even modern gear develops issues and instability when overheating. When I first got my MOTU 828 Mk3 interface many years ago, I put it flat on my desk. I noticed it was getting really warm underneath it but thought it was normal so I kept it that way. It only took a week before it started acting crazy and had to be returned for a replacement.
I decided that from now on, I was going to treat every piece of gear with consideration of the way they were built. I used some of my vintage (early 80’s) family Cuisenaire rods. The red ones are all exactly 2 centimetres long. I glued them with a little bit of hot glue and used little square pieces of felt pads to make sure everything is smooth and doesn’t leave marks on surfaces. I’m keeping my gear fresh and stable this way. I do this with each device that tends to accumulate heat, including the MOTU 828 on top of the S950.