"allow me to open the .tax file and add the crypto CSVs"
TurboTax CD/download program does not support import of a csv transaction file.
Instead, proceed as follows.
Adjust your csv files so the columns are in the same order as on Form 8949.
Put a header with your name tax year and SS Number
Use the summary option and then you can mail in the printout of the CSV files.
At tax time, you have the option to summarize your transactions by Sales Category.
IRS requires C/F details to be listed on your own Form 8949,
or on your other forms (e.g. spreadsheets) which have the same information and in the same manner as Form 8949.
Either way, if you choose to summarize, you have to mail the transaction details to the IRS within three business days of IRS accepting your e-Filed tax return.
Since you will be filing on paper for a prior year, attach the spreadsheet details to your amended tax return.
