there really isnt a specific filter for MARCS, doesnt really work that way, first the biggest thing is reception so you have to look at these areas as well.
1. Radio Location
2. Signal Strength
3. Antenna
the filter will clean up the audio but if you have a garbage signal no filtering will correct that.
being said the wide-invert filter works well for me the key is to keep the digital errors as close to 0 as possible