Hi Simon,
Multilayer accounting is complex as we all know.
What I understand from your requirements is what if you use “None” layer to post transactions.
Yes, I have done implementation with same scenario.
What I had done was user posted acquisition and disposal using derived book setup and depreciation will be posted using separate journals specific to each layer.
As depression posted using layer “None” there is no impact on General Ledger.
So at the end of specific period user have to run a report called “Fixed Assets Book compare” reports to identify the difference of transactions posted using “current” layer which was posted in General Ledger and “None” layer which wasn’t posted in GL.
So now user will pass entry of different value in general journal or FA Journal with TAX layer.
This will provide TB as required. (Run using Current + TAX)
Let me know it works for you.
Thanks,
Gaurangkumar Jani