Really worried that you are having him castrated at such a young age, why? You don't yet know what his real temperament will be and if he's fear reactive it is likely to exacerbate his anxieties
Burrs are best removed with a Coatking or Mikki Matt splitter/Matt buster - that and equinne silky mane and tail we find the sticky buds just glide out.
Please don't muzzle him - again, his only means of telling you he's uncomfortable is the way he has - how would you like your hair pulled and restrained whilst it's done? He's six months old and has a massive amount of maturing to do yet, his growth plates are not yet closed (c14 months), his hearing isn't fully developed (c10 months) and his ability to control his own impulse (think toddler and fingers in sockets) won't happen until he's between 23 months and three years old! If he's finding the grooming experience too much then I would suggest short bursts of 5 minutes only - he may still have burrs but he'll be a whole lot happier.
Sorry, but whoever has told you Cockers calm down with castration or spaying was fibbing........This forum has a wealth of advice on previous posts and we are all here to help. My first cocker had me mentally and physically exhausted when she was 9 months old - we now have four cockers and I think I have a pretty good understanding of the breed.
IMO the only winner in castrating a dog so young is the Vet who is guaranteed a wage - unless there is a valid medical reason that he should be?
Welcome to the forum - sorry if my reply is a bit terse but your post seems to only be focussed on you, not the welfare of your pup
Jayne