Unless the trademark name is registered, you may not much to fight with.
While I'm not an attorney, I do have 3 US patents, and clearly, the guy who get's his name, or phrase or slogan registered, is the clear cut winner.
Rather then duke it out with Bob, I'd also suggest a phone call and see what that will lead to. Bob's amps are in the Music Direct catalog, and the title is
"Cherry 180 Monoblocks". I guess he did use the name Cherry, but he also used the quantifier, "180" in his product title, so IMHO, you do not have a naming conflict.
I'd let it go...............
Wayner