Sue,
the clue to initial desensitising to type/breed lies in Chris's post: Cherchez la femme!
Find an amenable lady Rottie [we asked our vet if he'd be kind and let any nice lady dog owners know our 'phone number for a meet and he found two - one of whom we knew on walks, but didn't know their number!] and arrange to meet somewhere open. No leads. Let the lady do the talking and if he'll play with her you're past the first hurdle of see-black-and-tan =

Try and make it a fun occasion for all of you.... nice day, nice walk, treats.... perhaps drink together afterwards - the whole ambience and aftermath has to be full of good vibes.
I'd aim to do that a couple of times with just Max, then introduce our Geriatric Pin-Up. If he fouls up the friendship, Max may just see that for himself! It can't be bad, either way.
When Max is comfy with the see black-and-tan and doesn't assume instant posture of defensive aggression/tail wagging (which can still be defensive! no all tail movement is totally agreeable) then, and only then, can you introduce
Rotties of the male sort..... and even then I'd aim to start with a neutered one!
