I'm super keen for this to take off! looking forward to impressions as hoping this could finally be my electrostatic

I'm not exactly sure what your question is but that set up should sound as good as most other set ups in that price range. Is the bifrost going to be an original bifrost or an uber or multibit? 

Experience - Kacy Hill

The magni might give more punch but shouldn't add to the 'amount' of bass. You may want to try the Hd650, basically a HD600 with a bit of midbass boost. 

Definitely upgrade headphones. Maybe fidelio x2 or hd600 but the he-400i would probably be my first choice. 

I second the fidelio x2. You may even want to try the fidelio x1 if cheaper and would still give you the sound you want. Maybe you could find a used pair of fostex th-X00 for $300? But that would be a great deal. 

Does anyone know the Australian release date for this? Or pricing for aus stock?

  The original cable felt a bit stiff so I upgraded to a CustomCans cable for 79 euros. It feels much better and has really nice build quality. Didn't change the sound though so without auditioning I definitely wouldn't put any more money than this into the cable. 

Checking my source like this helped me with a similar problem. I felt stupid but it was that the balance on the sound output on my mac was skewed to the right. Just something to check. 

Would separates be okay with you? That way you can upgrade them individually down the track. Maybe  Schiit Modi2/Magni2 combo for $200? Even better I would suggest buying used so you can save cash. 

I just bought a pair of the KZ zs3 and I love them. You can get them for $10 and they sound as good as most $50 IEMs. Depends what sound signature you're looking for. 

I don't know anything about the on-ears, but I had a pair of the over ears and they didn't leak much sound at all. Up there with the least leaky headphones that I've owned. 

I'm sometimes in Goa and haven't seen any high end audio there previously. Is there any places I'm overlooking? I currently have a pair of HD800.

That DAC is fairly good. Most improvements from there would be relatively small. If you haven't done it already, maybe optimise the room acoustics because I think that it might make a bigger difference.