I 100% agree with your tyre comments, my point is there ARE cheaper options out there, so dont be put off buying a 19" wheel just because a 235/40/19 tyre is hard to come by, it is not, they are out there whether it be a budget or a higher grade. They will both have to pass the "speed rateing", and the budgets that i was quoted for, did indeed have the same rateing as their more expensive counterparts.
I think the question regarding the sensor valves was, "can the system be tested WITHOUT deflating the tyre". Removing the wheel is an option but this will only indicate that the onboard display has lost contact with the valve sensor, it does not indicate a drop in pressure on the tyre. It's basicaly alrming as it cannot find a signal from the valve, because it has been removed outside it's signal range, if you took the wheel off and kept it close to the car you then probably find a signal again ?
I think then to get a true alarm, indicating loss of pressure, you have to deflate the tyre, watching the display to see when it activates, then take the tyre pressure reading, you can then use the onboard compressor to re-inflate the tyre.