I *think* that if your MCU Pro shows firmware V 3. When it powers up it is a Pre 2010 model with the Penny & Giles faders for which V3 is the last version. No need to update. If it shows V 2 I recall a new EPROM had to bought from Mackie to update to V3. I still have the old chips in my studio drawer!
The post 2010 units ship with V4 firmware to accommodate Alps faders which were used instead.
Happy to be corrected or updated on the situation but Mackie isn't the company it used to be and info is hard to come by.
Cubase 6, Nuendo 5, MacPro, OS10.6.6,