Hi
In a previous post you mentioned having other cats as well. How many do you have and how many litter boxes? It should be one per cat plus a spare. Whilst most cats might not be particular about litter type, one of my Bengals most certainly is! And also will only use the litter box he made me move from the conservatory to the hall. Much to the other half's disgust. He will also only use it if it is literally spotless. Hendrix is not so particular. If there is another wee in there, he will still use it. Jagger won't. And he will only use the litter that is incredibly heavy - clay based clumping litter that closely resembles sand. We had used a different type for a good couple of years before but I changed it to see if it would make a difference and now he will use it without so much fuss and no out of box incidents.
So when he goes outside the box, is there anything else at all in there from another cat from your household? I sometimes have to put a fresh layer of litter on for Jagger to entice him to use it if he's making a huge fuss. We have two large boxes but both prefer the hall one unfortunately and Jagger considers this his and will guard it if he thinks Hendrix wants to use it for a poop
If there's still blood in his stool he may associate the litter box with pain if it hurts him to go so worth getting him checked out again. Hendrix used to have blood in his stool and I give him a probiotic every day and also changed his food to something really easy to digest as he seems to have a reaction to certain things which causes the bleeding.
Stress can also be a factor with litter box issues. I think you said he beats all your other cats up - how is his relationship with them these days? Has it improved at all??
It is definitely worth speaking to your vet. They may be able to offer some advice if behaviour or stress related, it takes time and patience though to work out what it is that's bothering them - you may need a referral to a behaviourist if all else fails. He's still young so you need to crack this before it becomes a habit.
Hope some of this helps!