The ARKYM sits above the felt boxes (based on pictures I've seen). How about the Challenge?
Does either lip present issues with clearance? I wouldn't want something that's constantly scraping speed bumps and ends of driveways.
2011.5 M3 Coupe: Space Gray, 4MY, ZCP, ZCV, ZP2, 494, 5AC, 655, and 752
Mods: Full Venture Shield protection kit, RPi scoops, Euro fog light switch, LUX V4, clear reflectors, OEM black chrome grilles and side gills, black hood vents, IND F10 M5 shift knob and boot