Jeez to be honest I have never payed duty fees to an external company.
When the duty and custom fees are included in the shipping you will pay a once off fee usually.
If they shipped it via Buffalo without paying thr customs then the South African Customs office usually sends you a message with...
In my case I have opted to go the PC route with my entertainment system.
I have backed up about 15tb worth of 4K dolby HDR movies on my small Asus Mini PC and use Servio to create a streaming server in my home using the wifi network.
Toslink input to my DAC and VSFilter running with MADVR...
ITunes have a Burn disc button...
The same also applies to the other streaming services. I have burned many HD discs using these functions. There are some limitations but it works
Also when you order from BestBuy or other sites the digital copy is included.
This makes it possible to transfer your purchased Bluray disc to any hard drive or disc.
Example from BestBuy
Just look for the "digital copy included" wording in the title on Amazon or any other retailer
Amazon...
I think it would be cheaper and less of a hassle to buy them digitally and write them to Bluray or 4k Disc.
External Bluray writers are available.
Like this one in the below link...
BobShop - External Bluray Writer
Bluray and HD disks are available in different quality and quantities
I had a similar issue but it turned out to be the System board thats the culprit.
When my new security company took over they didn't replace the existing board and just programmed it for their use and comms to their systems...
Because it's still a oldish system that was installed it drew more...
I am going to say that I found especially with Amplifiers that grounding loops seem to be the most common low audio quality culprit for me.
Had a horrible time trying to remove a constant humming on my active subwoofers on more than one setup...
Tried high quality cables and all the possible...