The KI203, KI208, KI204, & KI209 indicators feature an internal VOR/ LOC converter and are compatible with the KX155 transceiver. The KI203 & KI204 have rectilinear meter movement, while the KI208 & KI209 feature pivot needle action. The KI206 has rectilinear meter movement and works with the KX165 & KNS80. The KI209 includes GPS interface capability.
The KI 203 VOR/LOC Indicator with built-in VOR/LOC converter and scallop rejection filter has rectilinear needle action and an optically coated glass lens. Dimensions: 3.25" X 3.25" X 9.85"
Per the Garmin install manual, yes the KI 203 CDI will work.
Yes the KI 203 will function with the KX125.