Avoid random Google Drive links from unknown blogs. Instead, use:
A: Yes, the Amlogic SDK officially supports Android 5.1 Lollipop for S805 chips. However, official firmware with Android 5.1 is rare for generic MXQ boxes. mxq s805 firmware 5.1 download
If your box still boots, go to Settings > About MediaBox (or similar). Note the Model Number (e.g., m201 ) and Build Number (e.g., KOt49H.20150720 ). This is the first clue to finding compatible firmware. Avoid random Google Drive links from unknown blogs