Neutering will reduce his aggressiveness no doubt because he's no longer frustrated at not being able to find a mate, but it doesn't teach him that you're the boss.
From what you said, he definitely has dominant issue. Showing teeth and growling is pretty bad but can be fixable with a little persistence. Like I said, started by doing the little things, the most important ones:
- Shelter: All humans walk through the door first, including your guests. He doesn't go in until you invite him in. He will try to sneak in. "Kick" him out. Make him sit down and say "Wait" or something like that. You will have to repeat it again. Do so until he sit and wait without your presence. Then invite him in. You HAVE TO do it consistently. My dog now know to fully lay down and wait whenever I get home. The above also apply to your sofas/rooms/chairs.
- Food/ Water/ Toys: He does not eat when he's hungry. He eats whenever you want him to eat. Sounds cruel but in the dog world, the pack doesn't eat until the pack leader allow. You can set any feeding time you like but don't do it randomly, follow a routine. Now when you feed him, only offer the food if he's calm. He cannot jumping around. Make him sit down. Tell him to wait. Then wait until his eyes are off the food plate and on you. Yes, he must look at you. He cannot make any whining noise. Will take a long time at first but will work. When he's calm, put the plate down. He will try to go at the food. Do not allow that. He must wait until you offer him the food by saying "Go eat" or whatever. Do the same with food that was accidentally dropped on the floor. Food on the floor doesn't mean he can eat it because you haven't offer that to him. All of the above apply to water/toy. Occasionally, be a dick
and take away the food/toys while he's with them. Be careful and pay attention to his reaction so you don't get snapped. Use an object to protect yourself and just block him away from the food/toys. Make him sit down, stay calm and then offer them to him.
- Hiding under the furniture: Never allow him to go under the furniture at any time for any reason until his behavior changes. Dogs see such places as a place that can defend him against you. Sounds funny but it's true. He must not sleep under the furniture. He must not eat under the furniture. He must not play under the furniture. He can't even chill under the furniture. Block the place. You don't have to do it physically, just says no and "kick" him out whenever he tries to get under.
- Walking: You lead the way. Not him. He cannot sniff unless you slow down and allow him. He cannot stop unless you want to stop. Sounds cruel but again, think about the alpha dog.
- Urinating: Only punish him if you have taken him outside and he insist on releasing inside. If you haven't taken him out then it's not really his fault. If it's his fault, punish him by make him stay in a corner. Make sure you do right after he pooped so he knows what he's being punished for. Make him stay in the corner for I don't know 5 minutes. Nobody talk to him, play with him, call him during that time. If he moves from the spot, move him back and make him sit there. Call him whenever you're ready to forgive. try not to pet right away though.
The MOST important thing is you MUST NOT at all time, back away when he's showing teeth and growling. That is the sign of defeat and will not help.
All that reinforcement is great and all but will work better if you give him plenty of exercise. Walk him a lot. Give him something to kill time in the house. Mine loves the little squeaky toys and the dental bones but different dogs have different taste.
Watch the Mastering Leadership series. Everything I've learnt have been in there.