That RS5 sounded absolutely fantastic. They should all sounds like that, tbh. Was the RS5 discontinued after 2015? It doesn't seem to be an option on the current Audi USA website but maybe it is still available in other regions?
Or are they bringing a new one out like they are doing with the TT RS?
Edit - Answered my own question with a little Google search. New one will be turbo V6 (boooo!) http://blog.caranddriver.com/next-audi-rs5-to-get-turbo-six-and-possible-sportback-variant/
The NA V8 is gone so the new TTV6 RS5 is not going to sound anything like the B8.5 RS. I'm sure it'll be fast as heck but if I had to pick I would go with the V8.