Rainsoft 21179 RO System (6 yo) - Replace filters / system?

It is the proverbial annual maintenance time. My current Rainsoft 21179 RO system is now 6 years old (purchased in 2002). Given its age, which option is best overall....replace the filters, or replace the system? BTW, I live in Las Vegas, NV area.

If filters option, please recommend "brand", as my search netted me way too many options.

If system option, please recommend "brand". My current system is used for cooking, drinking (including 3 cats), and also supplies the water to the refrigerator's water line (ice & drinking water).

For H2O_MAN, would love to hear from you. Your diagnostic skills saved me HUGE a couple of years ago when my (both) Rainsoft timing systems went kaput.

Thanks!
Lainey