Every external keyboard sends a scancode which is unique for every key. Flirc is basically an external keyboard. So if you program it to send e.g. the key "a" for a specific button of your remote you can let the app "external keyboard helper" translate the incoming "a" to whatever other keypress you want, including all Android Keycodes (like Volume up, volume down, next track etc. etc.) There is an other thread in this forum whith a rather difficult method to get the special Media Keys of android to work with your Flirc.
External keyboard helper is an elegant alternative to that methode and you don't need to root your device.