First off kmeb--- everyone is very unique with food issues.
After searching Ensure...I can tell you that the maltodextin in there would
make me totally sick...I avoid that additive like the plague. Also carrageenan,
is hard for some people.

Benefiber is guar gum, and is a clear fiber, not a protein source.
There is a product Resource Beneprotein... is that what you meant?
I don't see why you could not mix either (depending on which you have)
into the Ensure...since you are "used" to Ensure.
When introducing a new thing, don't do a full portion. Start with only
a 10% addition, which is very small, and you might tolerate that.
Instead of juice I'd do 10% of the Beneprotein into Ensure once a day.
Then increase to 10% in two feedings the next day. Stop at any intolerance.
Coast for a while at your found comfort zone.

You must have adequate fat... without EFAs the body cannot maintain the
nervous system. I don't know why you can't digest fats...do you need
digestive enzymes? Have you tried them? It is not clear from Ensure how much omega-3 you are really getting...you should call them up and ask
for a gram amount/serving. They do not list it on their label. Since fat delays stomach emptying, you could add any additional EFA to the last swallow, which you saved for later, when the majority of the feeding is past time. You know how that goes..how long that takes. If the fat is taken away from volume you might tolerate it better.
It would be such a small volume, it would be easier to
tolerate that way...instead of a full stomach of liquid, that has delayed emptying. There is liquid flax oil you could try, in tiny incriments like with the protein powder.

Ensure is not meant to be a meal replacement 100% forever... it just does not have
all the nutrients we need daily. For temporary use, it is okay, but many
commerical formulas are not complete. An example is that in the preemie baby world they have just discovered that the TPN used for certain newborns was killing them because of inadequate omega-3 content. And this is after 20 yrs of experience with TPN (total parentaral nutrition given IV).

A "G" tube may work for you... there is a gal on another forum whose daughter with brain damage had one put in, and now she can go back to school. You do need technique, but it can be done.

None of the interventions/foods/made commercially can keep a person going forever. They all have limits, based on current knowledge. They get a bit better each year, but all have weaknesses.

You are seeing specialists, and I would only suggest at this time that
you try the things they offer, but only in very small amounts to work up
to a tolerable level.

I hope you find solutions soon.