For any other Aussies who need to avoid MSG and Aspartame (it triggers nasty headaches for me) or just want to avoid it when having protein supplements, especially during pre and post op liquid phases, I can recommend the following:

Choc-Hazelnut Formulite meal replacements are Stevia Sweetened (34g protein per serve is almost double that of Optifast, with fewer carbs).
NOTE: I can't stand the honeycomb one, but I assume it's something in the flavour as the choc-hazelnut is fine. I have a sample of vanilla on it's way to me to try soon too.
https://formulite.com.au/

Bodie'z clear protein waters are Stevia sweetened. Available in ready-to-drink bottles from some supplement stores and Chemist Warehouse. RTD flavours are kiwi fruit, berry (both 30g protein) and orange however sadly the orange is only 20g protein and has caffeine and guarana included so I avoid it. The RTD drinks are very smooth and easy to drink (taste like cordial/gatorade) and I'll be bringing some of these with me to hospital for post-op. Their powders are available as sample sachets and larger tubs in unflavored/unsweetened (though it still has a weird flavour, am hoping it will be ok in soups at least!), berry powder and an orange powder (the orange powder doesn't have caffeine or guarana added and I'm hoping it tastes like orange gatorade! I have a sample sachet to try soon).
https://www.supplementyourhealth.com.au/bodiez
https://www.pharmacyonline.com.au/search/go?w=bodie'z&ts=custom

I've also just found today a second Aussie-made protein water option called "Protein Perfection" which appears to be Splenda/Sucralose sweetened and you can order a sample pack of 7 sachets of the different flavours available for $15 with free shipping (I've just ordered the sample pack now!)
Flavours – Wild Raspberry/ Pina Colada/ Lemon Lime/ Mango/ Passionfruit/ Strawberry Kiwi / Icy Lemonade
https://costpricesupplements.com.au/products/1-protein-perfection-protein-water-sample-pack-6-different-flavours/

And the same brand makes a protein jelly in 5 of the flavours
https://costpricesupplements.com.au/products/1-protein-perfection-protein-jelly-5-servings/

I plan to order myself a pack of jelly and one or more larger tubs of the protein perfection powders once I've tried the flavours in the sample pack (they sound awesome!)

Cheers and best of luck to my fellow Aussie bariatric buddies!!!

Thanks for that!