tires make huge difference in road noise. old tires can be super noisy compared to new. road noise numbers are published by the automags for the various vehicles they test, might require manually checking each page however.
no comment/knowledge about aftermarket sound-deadening, except that it is sure to reduce mpg.
one aftermarket sounddeadening I vouch for is: new/proper/quiet tires. tire road noise is measured/rated by many web sites and tire experts. the most efficient tires are often the quietest - this is not a coincidence. look at michelin MXV4 perhaps...
final question about passenger conversation enhancement for hearing-impaired driver,via speaker system is quite intriguing . YES this is technically possible to do in an older vehicle with phono-plug or cassette-adapter, combined with proper microphone setup for the passenger. (noise-cancelling microphone/preamp/software/iphone-setti
ng). I am not aware of specific products/apps however. In newer vehicle it is also technically possible but with the small matter of software possibly being an impediment. For example, in my 2011 Chevy, the bluetooth connects nicely to iphone, but it won't arbitrarily operate through the car speakers except via phone call or specific "app" built into the car/dashboard itself.
With software changes, the exact functionality you request could be programmed into a base model new car like chevy cruze. There is little doubt that there are human-factors/engineering people at the various automakers working on such things and getting them to market - ask your favorite vehicle manufacturer and they may well route your question to the correct engineering/marketing department and maybe get you in a "focus group" for new products.
Current aftermarket products may well be available. Perhaps google-search using some of the keywords... best regards...