Glad to help out where I can.
I look at it different than a lot of others. Some think you should make your request only 1 way. I do not. I think you can make it as many ways as you want, as long as they are all exactly the same. If you can do that, there won't be any risk of confusion. And, if one method doesn't work, or stick, then another stands getting through.
For instance, if the fax fails for some reason (because let's face it, we all know fax machines do fail, paper or electronic) or if the MDX request glitches (because let's face it, we've all seen glitches on MDX) or if you call and the request made via phone doesn't get saved (yes, sometimes they do get lost off the reservation)
So I would indeed use the fax service to request a room and then use online check in and check a box that also matches features the room has (if the choices match). I rarely call and add any requests since mine are never specific enough to need to call.