Originally Posted by Ben628

1. What can I do to reduce the drone or sound without restricting it with the silencer?

An exhaust shop such as Metthams Mufflers, Carline Automotive & Exhaust etc can install a resonator or small muffler to your exhaust. This will bring the noise back down and shouldn't be too restrictive - no matter what though, anything you install to the exhaust that isn't a straight bit of pipe is going to increase restriction somewhat.

2. If nothing can be done, since the old silencer has been destroyed, is this something that can be purchased again separately?

If it's a silencer that slips in the end of the exhaust tip then yes, they can be. XForce silencers can be sourced from one of their Perth distributors (Metthams Mufflers is a distributor or checkout their site; Where to Buy)

3. I've read a lot of people saying that once we install the equal length header then the Subaru drone / rumble is gone and it will be a lot quieter and in fact have better flow than unequal length header, is this true?

Equal length headers will reduce the boxer rumble and will flow better, but I don't think you'll see a volume decrease - if anything it'll be an increase. 2.0L cars will also require a 2.5L oil sump to make them fit.

4. If option 3 above is a good path to go, I've seen around and Empire Performance seems to be the most cost effective one, have any of you guys have experience with this product?

There have been some TOG equal length headers with a 2.5L sump to suit and oil pick up advertised on Subaru Owners WA on Facebook etc for $500. I'd be going that way if they're still available. Ultrex Performance also offer unequal and equal length options, these are top notch quality and well worth the price difference to other options.