No, I wouldn't switch from the Equine Senior either--it's what I had in mind. It is a complete senior feed.
If he won't eat it wet, try just adding a tiny amount of water at first--stir it around to make sure that all of the pellets get damp as this helps soften them. Many horses will balk at a sudden serious change in texture but if you do it slowly they won't mind. I had to start our old man out slowly on the wet senior but now he likes it just fine.
The compressed alfalfa may be part of the blockage problem because forage and especially dried forage requires serious chewing in order to digest well. Equine Senior is designed to provide all the fiber necessary in a horse's diet, so you could cut out the alfalfa and just increase the amount of Senior he gets. It will keep the diet balanced as well.
Licensed Veterinary Technician