I think one of the strongest is your wanting to know if the therapy is working.
I disagree. That will not carry any weight with the DME.
I think it is a mistake to surrender authority over your therapy, RM, by allowing them to think that you must convince them to give you the machine you want.
I gave the girl all the info on how i need to keep my data
Why would you do that? That tenders veto power to her. You don't want that.
I think your better tactic is to either get the prescription written as Slinky suggested, then take a COPY ONLY of it into the DME and insist that the dispense as written. If they balk, do not stray into arguments about how you want to track your own therapy--they don't think you ought to be doing that in the first place, so you are just giving them reason to refuse to give you what you want.
Do not use any argument other than "this is the machine my doctor has prescribed." Some questions you might use:
"Are you telling me that you are refusing to fill the prescription as ordered by my doctor? Do you have authority to override her judgment?"
"Are you going to fill my prescription as written or not?"
"What machine does my prescription, as written by my doctor, call for?"
"Which machines do you have that match this prescription? Does that one record efficacy data?"
Each time they give you the runaround, ask a question like the ones above. DO NOT ANSWER their questions about why you need a certain machine.
THEM: "Why do you need a machine that if fully data capable?"
YOU: "Are you going to give me a machine that is consistent with my prescription or not?"
THEM: "It depends. I need to know first why you need that machine."
YOU: "Are you suggesting that whether or not you give me the machine my doctor has prescribed depends upon my answer to your question?"
Answer every question with a question. If you are psychologically incapable of doing that (and I was when I was younger), then the only acceptable answer is something along the lines of "Because that's the machine my doctor has specified."
What I would do, actually, is fax the prescription to them first. Then I would call and ask them if they have a machine matching the prescription ready for you to pick up, and if so, you'll bring yours in for the exchange. If they say yes, ask what make and model it is. Then post it here and let people tell you whether that's one of the ones you want. If it's not, call them back and tell them it doesn't match the prescription--we'll tell you why if you give us the details of the prescription.
If you can't get the prescription, then it will be tougher, but I would tell them you don't want the current machine, you want to exchange it for a <S8 auto> or whatever the name of the one you want is. They will decline. You ask them why they are refusing to exchange machines for the one you want. Point out that the one you want matches your prescription. "The ..... machine matches my prescription, and it's the one I want. Do you have one of those? If not, what machines do you have that are fully data capable?" I'd do it over the phone until you get agreement.
As people said, be firm but diplomatic. NEVER EVER be drawn into a discussion of whether you NEED that machine. If they say, "You don't need a .... machine, the Escape will do fine" then I would say, "No, that is not the machine I want. I want the .... machine, which my prescription allows. Will you give me that one or not?" You will NEVER convince them that you need a fully data capable machine, so don't try.
Don't forget, you can do this in multiple conversations, especially if you are exceedingly polite. If you start to feel frustrated, tell them you need to go but will call them back. Take some time to get your mind straight and calm, and then call again.
Good luck, and don't get discouraged.