Q0101,
I believe you are placing far too much confidence in biology as being an optimum medium for sentience. Also, there is nothing special about emotions that bar them from being experienced by a non biological machine. At the core of sentience is the processing power of the brain. This has some 200 billion neurons and there are more variations of neuron than any other cell type in the human body, but even so they all have essentially the same very simple characteristic. They have 100s to thousands of inputs from other neurons and deliver a single output. A neuron is in essence a slow microprocessor with a clock speed of around 300Hz. What makes the brain so powerful is that all these tiny processors are operating independently and in parallel. But the connections between these units are slow chemical synapses, again not very fast.
Exactly how the signals between the neurons result in sentience and what we call emotions is obviously the challenge for the upload designer. But the essential unit of processing is simple but it is just the vast number that is daunting. For us to do the same we’d need some 10,000 tightly linked high end computers to come close. Something we will be able to do within a few years.
The biochemical reactions you describe all result in data signals to the brain. Emotions are data signals also that result from other hormone and related body processes as well as thoughts, e.g. other signals from the brain. In the end it is the brain that is processing data that we experience.
I think our biggest problem here is trying to imagine how such an engine can result in self-awareness and sentience, i.e. vital characteristics that we cannot clearly define. Until we really understand these then I don’t think you are in any way safe to assert that an electronic non-biological engine cannot do the same as a biological processing engine.