Exhaust modification without Dyno tune?

Hi all I'm thinking about modifying my exhaust due to how loud it is. Not entirely sure on the system looks like 2 3/4 or 3 inch pipe with a pre muffler and cat with an enormous glass back cannon. Volume isn't too bad except when the engine is under load or crusing at certain speeds, going up hills etc and it hits a very deep bass note that reverberates in the cab, gives you a headache after awhile.

Willing to suffer s few HP losses in the top end, but not much! Mechanic who does a lot of Subaru Performance stuff wants to measure it up, I know its not as simple as wracking any old muffler on.

My question is will he be able to do a reasonable job with out a dyno? I know he 'street' tunes and then hires the dyno afterwards but should I just go to the place with an all-wheel drive dyno?

Also, am thinking of putting a different ecu later on and adding another 50-100 bhp, not sure if restricting the exhaust a bit will be a problem later on.

Currently running - ST185 with a ST205 motor, FMIC, extra volume fuel pump, Garret Disco Potato Turbo, stock ecu.

Add a high flow resonator, it won't effect hoarsepower at your mod level. Im not sure what you mean about street or dyno tuning with your setup? Do you have a wideband and a boost controller? thats about what you need to boost tune, as you can't adjust the ecu.
Make the car quiet and more enjoyable and driving the piss out of it!

'street tune' was doing it without a dyno supposedly . I agree from the reading i've done the resonator seems like the best option. The only other thing i've been looking at is an xforce Varex muffler: has a buterfly vale on a electric motor which sets it at either unrestricted or a chambered muffler, supposedly takes about 20dbs off. Bit tempting, values at $400 australian probably closer to $600 installed. Best of both worlds?

Why would you be dyno tuning a basically stock setup because of an exhaust change? 3" pipe is overkill for these cars anyways, so the car will not notice a little bit of restriction added back in.