90% of the extra sound in a catback system comes from going catless in the midpipe - thus best bang for buck exhaust mod is midpipe only
the best sound (and power) comes when you go catless on the downpipes, and you won't really understand how much better it sounds until you do it
muffler only is really just increasing the volume of a bottle knecked system. I know because i did my exhaust in 3 stages - catless midpipe (great sound), muffler (slight increase volume only) and lastly catless dp's (complete change in tone, more raspy, more burble crackle/pop on overun, significantly improved turbo spool)
i was initially looking at spending 7k on the amuse system but what stopped me is the GTR tax - Amuse charge half that for the 370Z system which includes more ti and more mufflers, and that's just taking the piss
someone only recently pointed out my 997 gt2 has an akro exhaust from oem, so i guess that's given them the excuse to jump on the GTR tax bandwagon
i spent just over 2k for my cat back, looks fantastic and works even better. Been running it for almost a year now with no discoloration of the ti. One of the best buys i've ever made mod'ing cars.
each to their own, this is just one person's feedback