Nowadays, too many reasons make modems to become rare.
A lot of people have a multifunctions printer with Fax capabilities, and so I am.
Using MFC printers on differents sites, I'm facing the lack of a true Linux faxing application from Brother.
Faxing with a Brother network printer needs differents steps :
1°) create a Postscript file from any application
2°) from command line, start the main script provided by Brother with some parameters
This main script is responsible of :
1°) getting the Fax destination number if missing (a graphical java utility is provided)
2°) sending datas to a fixed name CUPS queue (BRFAX)
Note that faxing this way, you have no header line, so I wrote my own macros in OpenOffice but how to do with any other application ?
efax-gtk knows how to receive files on a socket, let the user select the fax destination number from the Address Book and then use the script efax for sending.
Would it be reasonable to imagine a new ??fax-gtk version becoming the graphical interface for Brother brpcfax script ?
The efax-gtk program would not be a great deal of help with what you want to do, I am afraid.
If you want to insert a top header in each page of an existing postscript document, probably the best thing is to render each page of the postscript document to a cairo surface (libspectre would make this reasonably easy), scale it to leave a gap at the top, then use cairo or pango-cairo to insert the header text at the top of the page, and then render the amended page to another postscript cairo surface for output.
But efax-gtk will not help with this.
like you, I think that replacing the whole scope of brpcfax script is not a good idea : this is the job of Brother and if there is no top header line, it remains their problem.
My purpose was only to ask for the ability of your graphical interface to have a useful place between the user and the script "made in Brother".