You are comparing apples with oranges. The MX5 contains a power amplifier (to drive passive speakers), the EX5 does not. The EX5 has line outputs to drive a power amplifier or powered/active speakers, the MX5 does not.
You mention RCA output being a benefit, which suggests that you already have powered/active speakers. If you are happy with your existing speakers and have no plans/desire to switch to passive speakers, then you have no need for the amplifier in the MX5. The EX5 works perfectly as a pre-amp (volume control) for a pair of active speakers (that's how I use it).
Also, it doesn't matter which one is newer! Would it be better to tighten a screw with a new hammer or an old screwdriver?
The display on the EX5 is an orange backlit LCD. It's very unobtrusive and easy on the eye in a wide range of lighting conditions. I appreciate this because my EX5 sits about 50cm in front of me under my computer monitor.