1, Take course on feedback fuel injection then measure signal with DVOM. (Sorry, answer w a y too long to post)
2, Disconnecting or modifing a HO2S is violation of federal law, and would result in zero gain anyway.
3, Bad knock sensor would probably set code, would not make it advance too much anyway. Does it ping? Testing limited, verify good wiring to/from DI ECM if okay test with new sensor.
4, Glowing exhaust sounds like too much oxygen, like when you blow on coals. Look for causes of lean mixture or high temps.
5, If you need a sensor, buy a genuine Bosch sensor from Bosch retailer specific to your Volvo or from dealer, regardless of cost.
6, All that heat is also baking rest of engine parts, i.e. cooling system hoses, a/c etc. adding to repairs if delayed further.