Husband sleeps almost all day and night. Any thoughts?

take him to another cardiologist and neurologist for a second opinion. he may have physical problems that the doctor is missing or he may be overmedicated. this happened with my husband and was not picked up until we moved and changed doctors.

Any chance he could have sleep apnea?

If everything checks out health wise it is possible that the excess sleeping is boredom and or depression.
Can he use a Tablet? There are some that have been configured with words and can be used to have conversation. Medical Speaking App would be what I would search for.
Has he tried ASL (American Sign Language) or does he have a problem with manipulating his hands?
Have you looked into Adult Day Care or programs at your local Senior Center? If he is social that might be just the thing for him.
How about Volunteering? The Hospice I volunteer with has lots of things to do that do not require verbal communication. Many do not require writing. If he can use a computer that would be good.
Animal Shelters need volunteers that will walk dogs, play with cats, clean pens (I know not glamorous but someone has to do it.

Giving him Boost or other protein drinks is more calories. If he is eating fine and it is just the sleeping I would think boredom or depression so I do not think drinks will help.

I certainly can relate to your situation. My husband had a massive stroke at the age of 48, which also left him unable to speak and write. He eventually could say a few words and some short sentences, but we really could never have much of a conversation. It's hard, I know.
My husband also lost use of his right arm(he was right handed)and had to learn how to walk again, with the use of a brace on his leg.
I kept my husband at home with me until he died last Sept. at the age of 72. He at that time had developed vascular dementia, and went downhill from there.
Your husband is at risk for that as well. Have you talked to his neurologist about that? If not, you may want to.
Now as far as the Boost is concerned, it certainly won't hurt him, that's for sure, but whether or not it will help him with his breathing I highly doubt. I would instead take him for a second opinion to try and get to the bottom of exactly what is going on. And you may even ask his Dr. about getting hospice involved at this point, since he's sleeping so much.
My husband slept about 16-20 hours a day in his last 6 months of his life, and was under hospice care the last 22 months of his life.
I hope and pray that you will be able to find out exactly what is going on with your husband. Best wishes.