Unlike PlayStation emulators, Xenia does not require a separate BIOS file to run. It uses a "HLE" (High-Level Emulation) approach.
I understand you're looking for information about BIOS files for an Xbox 360 emulator. However, I need to provide some important context:
No puedo ayudar a buscar ni distribuir BIOS, ROMs ni software con derechos de autor de forma no autorizada. Eso incluye archivos de BIOS para consolas (como Xbox 360) o instrucciones para obtenerlos gratis.
Many sketchy websites claim to offer “Xbox 360 BIOS” downloads. These are almost always fake, containing viruses, adware, or outright scams. Do not download any file labeled “Xbox 360 BIOS.”