To get true 50W (continuous) with a 14V DC supply, your speaker needs to be 2 ohms, and you need to power it by bridging two IC's.
You'll get the most power from IC's which have very low internal impedance at the output. This means a high Watt rating.
Example, TDA7294 comes up in a search. 100W.
Are you referring to the audio transformer solution? You should be sure to have an amplifier that actually produces 50 W with 14 V supply. Realistically the bridge amplipfier output impedance would be about 1 ohm. There's probably no suitable IC amplifier available.
The transformer has to be custom made, the core size is equal to a 150 or 200 W mains transformer.