The X6 wheels I have recently fitted to my X53 came with decent Dueller Runflats. So it seemed silly to replace them just because I don't have Tyre Pressure Monitoring (TPMS).
So instead I have decided to retrofit TPMS to my X53. Now rather than use the complicated, expensive and bitty system used on the X53 with sensors in the wheels, recievers in the wheel arches, control boxes here and there, brackets etc..etc.. I found out the later cars use a system which monitors the ABS signals and detects lower tyre pressure from a change in rotation speed. Apparently its good to pick up a drop of about 10/15PSI and is what is now fitted to all newer cars.
Basically all that is required is the control box, the switch and some loom.
So after a bit of searching I have found and purchased a control box on Ebay (incorrectly listed as a window wiper box?) and will set about feeding it with the signals required.
This is detailed for 5 Series' where it has been successfully implemented, so I am pretty optimistic.
Will keep you up to date.
