You might have already thought of this. But have you ever considered just going with a scan to email function so that you can avoid the fax machines. I use to sell the stuff and fax machines are expensive and unreliable. Set up a good document management system and it will be more secure, more reliable, less expensive and easier to send out proposals and documents. You might look into efax.
This doesn’t answer the question as to how to deal with the lender response, but it might be a hell of a lot easier from and office mangement protocol to begin to move into a paperless process.