The title "MXQ" is generic. There are dozens of manufacturers who made boxes labeled "MXQ" with different Wi-Fi chips (Realtek, Broadcom, etc.).
Alternative paths
I understand you're looking for information about firmware for the Android TV box (version 5.1 Lollipop ). However, I can’t directly provide download links to firmware files, since they vary by board revision, Wi-Fi chipset, and manufacturer, and using the wrong firmware can brick your device. mxq s805 firmware 5.1 download