So scenario 1: You chain IMT to
Soul Exchange and unless you have another monster on the field the conditions would not exist for your opponent to activate
Tribute Doll at all.
Scenario 2: You activate a response chain to
Soul Exchange resolving and unless your opponent has something like
Mystik Wok or an already face-up
Ultimate Offering your X-Head will still be RFP before your opponent could activate
Tribute Doll, thus there wouldn't be a chance for him to use
Tribute Doll this way either.
Scenario 3:
Soul Exchange has already resolved and your opponent activates
Tribute Doll sending your X-Head to the grave and you can't chain with IMT because it is not on the field to be targeted.
Pretty much any way you want to go (unless there are other cards on the field that haven't been included in your question at least 1 of these cards is being illegally activated.