Try switching to a more comfort oriented tire.
search online for reviews of each tyre you consider.
stick to the manufacture recommended size
This way you can keep the car original.
Mazda 6/attenza too belongs to same category as cefiro..
current generation is quite popular..
also Subaru legacy and Mitsubishi gallant fell into same group if I'm not wrong..
you can try fm band expanding device for fm radio...
they are available at car audio shops like petco
for the TV most likely cant. Japan is using NTSC while we are using PAL..
for Navigation system check with petco.. they may have a solution.. (petco is srilanka agent for kenwood)
try this
http://asia.yamaha.com/en/products/audio-visual/desktop-audio/mcr-b020/?mode=model
bit expensive... but overall quality is way better compared to other brands like philips
I'm using yamaha too.. highly satisfied..